How can I ask an unacquainted professor to collaborate with me? I have read several papers written by the professor and want to ask for him to collaborate with me, that is, to help revise my paper and finally make it publish.

I'm concerning with:

1) is it okay to do this?

2) how to effectively ask for help?

3) is it safe to deliver an unpublished work to others? 
If not appropriate, what can I do?

Any suggestions and help will be appreciated. Thanks!
There is no single answer to such a question as you deal with people. Regarding whether they will collaborate or not, it really depends on the professor, their style, their current available time to get involved in your work. 

But it is very unlikely that collaboration can happen without prior introduction in a venue, or through another third party who knows both of you. You can target a venue where they speak there, and approach them and chat with them to get some sense whether they are interested or not. Follow your heart in these matters. If you do not feel comfortable to the person or get a feeling they are not taking you seriously, forget about them and do not waste your time and ideas with them.

From your post, it seems you are almost done with your work and you want someone to revise it. This can be achieved by submitting your paper to a reputable conference, where experts in the fields are reviewers. You can check some venues where this professor you are interested in is reviewing (not guaranteed though, but if they are an active researcher in the field, they can be in the committee of some conferences. 

Is it safe to deliver unpublished work to others? Again, depends on the person. It is better to deliver it for official review where there are some rules governing the process and other parties involved.