Recently I find that the close/reopen vote threshold is reduced from 5 to 3 in StackOverflow. Will this feature be applied in this site? I think this feature will be really helpful because in this site, there are few users voting to close/reopen and I can hardly see a question is closed/reopened by 5 users (usually it is closed/reopened by a moderator).
No. Not unless we specifically ask for it.
If you would like to see the close/open threshold reduced to 3, it is my understanding that Stack Exchange is willing to try it out here if there is a strong agreement here in favor of that. But, we have to go through the process.
So, if you'd like to see that happen, start a new question, ask whether the threshold should be changed, post an answer saying "yes" and why, and let people vote on it. If there's strong support for it, I'll get in touch with the Stack Exchange folks to ask them to make that change for us. I will need to be able to demonstrate to them that we went through the discussion process in the community and that there was strong support for this change, which is why posting such a question (separately) is the way to kick off that process.