I've told you guys many times that I love the mountains in Eastern China, but I can’t say I love them more than Mount Lu, even I've justthough I've been visiting Mount Lu for only a few hours.

The clouds over the mountains awere looking so heavy, look like it' was going to rain.

The waterfalls have so much water, flowing likas if they were shouting.

The clouds over the mountains are so heavy, and make it look like it's going to rain.

The flowers are livinglive in the middle of the mountains, too high up to be captured by my iPhone.

The waterfalls have so much water, flowing lik and sound like someone shouting.

Took a guess here. Not sure what the original sentence wants to say exactly.

There must beare probably many mistakes in this entry because I am too tired to check the grammar.

Oh I also took some videos and I will upload them when I am back toin Shanghai.

I've told you guys many times that I love the mountains in Eastern China, but I can’t say I love them more than Mount Lu, even though I've just been visiting Mount Lu for a few hours.

The clouds over the mountains are so heavy,dark. It looks like it's going to rain.

There are flowers are livgrowing in the middle of the mountains, too high to be captured by with my iPhone.

Saying "the flowers" sounds like you have already introduced them.
Changing the second part to active voice makes it sound more natural.

The waterfalls have so much water, flowing like shoutingoudly.

Oh, I took some videos, and I will upload them when I am back toin Shanghai.

When you are connecting two independent clauses with 'and', you need a comma before 'and'. An independent clause means it could be a sentence by itself.
You could also write 'I took some videos and will upload them when I am back in Shanghai'. In this case, you wouldn't need a comma because 'will upload them when I am back in Shanghai' doesn't have a subject, so it isn't an independent clause.

I've told you guys many times that I love the mountains in Eastern China, but I can’t say I love them more than Mount Lu, even if I've just been visiting Mount Lu for a few hours.

"even" almost always has another word with it "even though" "even if" "even then" if it is connecting 2 clauses/sentences, only alone as an adjective/adverb

The clouds over the mountains are so heavy, it looks like it's going to rain.

The flowers are living in the middle ofgrow deep in the mountains, too high to be captured by my iPhone.

We don't usually say that plants "live" somewhere
It would be better to say "deep in the mountains," meaning it's very far up and in the trees, difficult for hikers to reach. I take it that's what you meant since you said "too high to be captured"

The waterfalls have so much water, flowingflow so powerfully, almost like shouting.

"have so much water" is strange since a waterfall is meant to have a lot of water

Oh, I took some videos and I will upload them when I am back toin Shanghai.

"when I am [back] IN Shanghai" use the preposition as if "back" was not there
similarly
"when I go [back] TO Shanghai"

I've told you guys many times that I love the mountains in Eastern China, but I can’t say I love them more than Mount Lu, even if I've just been visiting Mount Lu for a few hours.

The clouds over the mountains are so heavy,dense, so it looks like it's going to rain.

The flowers are livgrowing in the middle of the mountains, too high to be captured by my iPhone.

The waterfalls have so much water, flowing like shouting that their rushing sound is very loud.

There must be many mistakes in this entry because I am too tired to check the grammar.

Your writing is just fine!

Oh, I took some videos and I will upload them when I am back toin Shanghai.

Try to remember this:
going back TO Shanghai
I'm back IN Shanghai

I've told you guys many times that I love the mountains in Eastern China, but I can’t say I love them more than Mount Lu, even if I've just beenonly visitinged Mount Lu for a few hours.

The clouds over the mountains are so heavydense, look like it's going to rain.

heavy is fine, maybe dense is more specific.

The flowers are livgrowing in the middle of the mountains, too high to be captured by my iPhone.

The waterfalls have so much water, flowing like shouting.the flow sounds like shouting. (...is so loud.)

Oh, I took some videos and I will upload them when I am back toin Shanghai.