I join in several link exchange programs, and I get many inbound link from subpage of other site. These subpage are usually with low page rank. Is is useful for my site page rank?

I would delete all of your accounts on those exchange programs. Google is starting to ban sites that use them.

If you want to get links. Exchange manauly by contacting webmasters.
http://www.axandra-link-popularity-tool.com/index.htm
Or buy them.

Agreed. BUt I am also looking at a 2 proged approach. I have started to launch sites just for MSN and Yahoo. THen others for Google. YOu can get immediate results with MSN and then work the Google angle over months since they run so many filters now.

Good advice from Montyx there!

thanks
I am thinking delete my exchange program

personally i wouldn't panic too much about being banned however these link exchange programs are little (if any) worth to SEO

Digging up posts from 5 years ago is likely to result in getting banned from here.