TheA survey shows that the success rate of quitting smoking only byusing perseverance can only reach 3%.

If multiple surveys show this, you could say "Surveys show that ..."

Although I don't smoke much, I have been smoking for decades, and I have always been on the way to give up smoking.

Your meaning is a little unclear:
Possible Meaning 1: You have always been trying to give up smoking, but you weren't successful in the past. In this case, you can say, "I have perpetually been trying, unsuccessfully, to give up smoking."

Possible Meaning 2: You have been in the process of giving up smoking for a long time, with gradual success. In this case, you can say, "I started the process of quitting smoking a long time ago."

Recently, I obviously realized that my body haswill not allowed me to smoke any more, so I must give up smoking.

I know I can't do it with my ownsolely using perseverance, so I checkedsearched for some auxiliary drugs on the Internet.

A starter pack is forlasts two weeks, but I quit smoking after eattaking it in the firstfor one week.

I never thought I was so stupid for smoking for decades!

If you mean to say you didn't realize the negative impact of smoking while you were a smoker, you have to say, "I never realized how stupid I was for smoking for decades!" Although, I don't think that makes you stupid - smoking is addictive and a hard habit to break!! Don't be so hard on yourself :)