I arrived at Shanghai but for me there are too many smokers on the road, entrances of subway stations, entrances of shops, and parks. Especially I hate those who smoke while walking on the road.

However, is there any outside place or district in Shanghai that you can avoid (most, if not all of) those smokers? For example, in Tokyo in Chiyoda Ward the smoking on the road is prohibited unless otherwise stated, and thus relatively few smokers can be seen there.

For your information I want to know the place or district or anything smaller unit that sees few smokers, irrespective of whether it is banned or not. For me the actual situation is far more important than the regulation, since I know the regulation only won't be effective at all, which is exactly the case in Tokyo (e.g. in Shinjuku and Minato it's banned but smokers don't obey the rule).

I want to base the area on my next trip to Shanghai. For my rough guess Xintiandi (新天地) might be the best, but that's just my tiny walking experiences...

Anyone knows any clues, if not backed by survey or statistics?

You'll have a hard time finding such a place, your best bet to avoid smokers is to avoid people.

Smoking is prevalent in China, let me start by quoting from the Wikipedia article dedicated to the topic (emphasis mine):

Smoking in China is prevalent, as the People's Republic of China is the world's largest consumer and producer of tobacco: there are 350 million Chinese smokers, and China produces 42% of the world's cigarettes. The China National Tobacco Corporation (中国烟草总公司 Zhōngguó Yāncǎo Zǒnggōngsī) is by sales the largest single manufacturer of tobacco products in the world and boasts a monopoly in Mainland China generating between 7 and 10% of government revenue. [...] Tobacco control legislation does exist, but public enforcement is rare to non-existent outside of the most highly internationalized cities, such as Shanghai and Beijing. [...] Furthermore, outside of the largest cities in China, smoking is considered socially acceptable anywhere at any time, even if it is technically illegal.

The article makes a distinction for large cities, but honestly, especially by foreigners, this is not felt.

So while the WHO applauds Shanghai for a proposed legislation to make public places smoke-free, do not expect much from it until it gets enforced. From a newspaper:

You wouldn't know it, but in 2010 Shanghai became one of very few cities in China to ban smoking in public areas. [...]

Yet to this day how often are we choked by cigarette smoke wafting over from someone's table at an eatery? How many times have we ironically seen someone lighting up right under a No Smoking sign? Or how about the jerk who walks into a crowded elevator obliviously puffing away while everyone around him is coughing and covering their mouths? No, it's not too hard to spot a smoker in Shanghai.

(I could back all of this from personal experience.)

The Shanghai section of the above cited Wikipedia article has some more info on why enforcement is low. Note that most of that was written in light of the 2010 Expo and focus has shifted away since.

In conclusion I am not aware of any open public areas (such as you describe in Tokyo) where a smoking ban is effective and enforced. So your best guess to avoid passive smoke is to avoid people, i.e. go to places where there are not only few people but also few locals. Good luck with that.