The connection check URL actually used is part of the update center metadata, see the comment.

You'll need to host your own update center and replace the URL with one that can be reached from your network.

@Daniel
In my update, I mentioned that I changed google url in source code, but still not work.
According to the logs I attached, this maybe lead to another problem. It seems connected to UpdateSite.java line no. 789
After some test, I found that "job" in "UpdateCenter.InstallationJob job = uc.getJob(dep);" returned null.

How would it be null then?

Why do you think that that value being null is a problem?

Did you change the connectionCheckUrl entry in updated/default.json (replace default by the update center name if you changed its configuration)? Because the hard-coded value you're referencing is never actually used...

Finally, I know what's the cause.
As you said, the log did nothing wrong.

It's due to two other hard-coded google urls:

Line 333 in method getConnectionCheckUrl() of UpdateSite.java:
if(dt==null) return "http://www.google.com/";

and

key-value "connectionCheckUrl": "http://www.google.com/" in $JENKINS_HOME/updates/default.json

This is a weird one.

On one hand, it makes sense to allow update centers to do their own connectivity check configuration, to account for corporate intranets. And it's a very rare situation that Google cannot be reached while still having actual connectivity, so it's a good default for the public update center. So I'd really like to resolve this as Won't Fix, unless you have a nice, generally applicable solution available.

OTOH, telling you to fix your network issues would lead nowhere. And I assume this affects all Chinese users, so a straightforward solution would be good. How easy (or difficult) would it be to route google.com to a host you can connect to, such as baidu, in your hosts file or local DNS?

I do not think changing hosts file is a good idea.

IMHO, the best solution at present is a graceful error notice appearing when checking connectivity hang there after some time. That notice should guide user to change the url in `key-value "connectionCheckUrl": "http://www.google.com/" in $JENKINS_HOME/updates/default.json `