Yes, I submit a support ticket, they said it's not a problem..
No, for the suggestions above,
I and my roommate have different steam accounts.
I close the firewall a long time before and I don't use any anti-virus software.
I reinstalled ETS2 and also TrucksMP, I'm sure I also delete all the documents in "my documents" at c disk..
It's very strange. I try to find the difference between me and my friend that he is a new player and I play multiple mode before, there is nothings difference besides this.
And I explain the issue again.
I enter the account name and password, I enter the profile screen and it says login successfully.
when I enter the game, it says connecting server and established. At the right top side of the screen, it shows no collision area, after I start my engine and begin to move, it shows offline immediately