The utility model provides a silencer for car exhaust system which includes casing, first baffle and second baffle, intake pipe and U -shaped pipe. Including lieing in in the casing expansion chamber between first, the second baffle. The intake pipe is equipped with the air inlet and extends and extension in the expansion chamber, be equipped with on the pipe wall of extension with a plurality of through -holes of expansion chamber intercommunication. The extension still be equipped with with port and part that the air inlet is relative are sealed half closure plate of port, wherein half closure plate semicircular in shape and shutoff are lived the latter half of port. The utility model discloses a set up half closure plate, when the exhaust of engine when the air inlet gets into the intake pipe, under of the stopping of half closure plate, partly exhaust is overflowed and is entered into the expansion chamber from the through -hole, another part is exhausted and is entered into the expansion chamber from the exhaust passage. So setting up, making the unlikely too much rising of mouth of pipe backpressure on the one hand, on the other hand also can effectively avoid the condensate return.