The invention discloses a silencer assembling device and belongs to the field of machining machines of silencers. The silencer assembling device comprises a baffle plate and a base and further comprises a first bearing plate, a second bearing plate, a telescopic rod, a sliding plate, a hydraulic device and a fixing rod, wherein the hydraulic device is fixedly arranged on the base through the fixing plate, and the baffle plate, the first bearing plate, the second bearing plate, the sliding plate and the hydraulic device are sequentially arranged on the base; the fixing rod is in parallel with the base and sequentially passes through the baffle plate, the first bearing plate, the second bearing plate, the sliding plate and the fixing plate of the hydraulic device; and after the telescopic rod passes through the sliding plate, one end of the telescopic rod is connected with the hydraulic device. According to the silencer assembling device with ribs disclosed by the invention, an air charging inner tube of the silencer can be quickly plugged into an expansion pipe so that a space between the air charging inner tube and the expansion pipe is small, the brazing filler metal is saved, the welding speed is quick, the efficiency is high, the realization of automation is facilitated, the welding cost is reduced, the connection effect is good, the appearance is attractive and the device is wearable.