The problem is that I was running fine yesterday, and today I added some code, and tomcat7 will start and crash. I removed the <Context /> in conf/server.xml, and tomcat started normally again!
So where is the problem?
I removed the code added this morning (a servlet, a jsp, and the <servlet> path configured in web.xml), restarted Tomcat, and it started normally.
Add all the code, this time tomcat can also start normally, it seems that the previous code is wrong!