In some cold areas in the winter of China, people would install iron chains on tires.

In some areas of China during cold winters, people install iron chains on their tires for safer driving in snowy weather.

So when a netizen from Niigata in Japan told me he was preparing new tires for his car, and that local people do the same thing in winter days.

So when a netizen from Niigata, Japan told me he was preparing new tires for his car, and that local people do the same in the wintertime, I thought "new tires" meant putting on iron chains.

I thought the "new tires" meant putting iron chains for securing safety in snowy days.

Combine w/previous

He told me they would change tires, and change back to regular ones when winter is over.

He told me they switch out the tires entirely and change back to regular ones when winter is over.

*Verb tense mismatch

They do this regularly every year.

Moreover, the policeman would be stationed at the the entrance to the highway assuring all vehicles' tires have been changed, or they would not be allowed into the highways.

Policemen are also stationed at every highway entrance to ensure that all vehicles' tires have been changed before permitting the cars onto the highway.

I think that this type of winter tires have better friction, traction and braking for safe driving in winter.

I think that their winter tires have better friction, traction, and braking, thus allowing for safer driving in winter.

In some cold areas in the winterDuring winter, in the cold areas of China, people would install iron chains on their tires.

Though what you said was mostly correct, I have changed it to sound more natural

So when a netizen from Niigata in Japan told me he was preparing new tires for his car, and that local people do the same thing induring winter days.,

This does not work as a full sentence on its own, you need the additional information from the next sentence for it to make sense.

I thought the "new tires" meant putting iron chains on for securing safety better grip during snowy days.

This sounds more natural, please let me know if my change does not make sense.

He told me they would change their tires, and then change them back to regular ones when winter is over.

They do this regularly every year.

You don't need to say regularly because every year implies this.

Moreover, theAlso, policemaen would bare stationed at the the entrance to the highway to assuringe all vehicles' tires have been changed, or they wouldare not be allowed inton the highways.

Moreover is a strange word choice here, moreover is a very formal word and you only see it in essays.

You should say policemen as it would be more than one policeman (police officer is also a common word to use)

'to check' may be a better choice than 'to assure' because it is less formal

I think that this type ofeir winter tires have better friction, and traction so they cand braking for safe drive better during win wintter weather.

This sounds more natural if you are referring to how the Japanese tires are different.