The invention proposes a main silencer for an air exhaust system of an automotive engine, which comprises a barrel body, an air inlet pipe, an air exhaust pipe, a medium-voltage cavity A, a low-voltage cavity B and a high-voltage cavity C; the barrel body consists of an inner barrel body, a first grid layer, a second grid layer and an outer barrel body; the first grid layer and the second grid layer are mutually crossed in a grid manner and are clamped between the inner barrel body and the outer barrel body in a two-layer superposition manner; a ventilation and drainage hole is arranged on the inner barrel body; and a drainage hole is arranged on the outer barrel body. The main silencer can prevent direct impact caused by high temperature and high pressure gas to the outer wall of the outer barrel body, reduce the vibration, the radiation noise and the effect on indoor comfort and simultaneously prevent the water accumulation generated in the inner barrel body to prevent a clapboard, an end cover, the air inlet pipe and the air exhaust pipe from being corroded by the water accumulation. Therefore, the comfort of the entire main silencer is improved, the maintenance cost of a user is saved, and the service life of the main silencer is greatly improved.