By some searching I found a solution to this problem.
First, change the DNS address in your network configurations to a better one, like google's 188.8.131.52.
sudo hostname theMachineNameYouWant in terminal.
The reason for this:
They say that when you are doing DNS lookup/reverse lookup, the DNS server can give your machine a host name, this function should be turned off for public DNS servers, but I don't know why the DNS server of my local ISP has it on.
Since my machine uses a router, so it has a IP like 192.168.0.x in LAN, I don't know why but when using traceroute, this IP will be sent to the DNS server for a reverse lookup, and since it is a reserved IP address, the DNS server returns a hostname as bogon, thus, changes my machine's hostname.
So what is bogon? Bogon means the type of IP addresses that should not appear in a traceroute, like a reserved IP address.
bogon on wikipedia.