The invention discloses a semi-active exhaust silencer which comprises a shell, an air inlet pipe, an internal insertion pipe and an exhaust pipe. The air inlet end on the shell is provided with a front end cover, the air outlet end on the shell is provided with a back end cover, a first separating plate and a second separating plate are arranged in the shell, a plurality of through holes are formed in the second separating plate, a first cavity is formed by the first separating plate, the front end cover and the inner side wall of the front section of the shell, a second cavity is formed by the second separating plate, the first separating plate and the inner side wall of the middle section of the shell, and a third cavity is formed by the back end cover, the second separating plate and the inner side wall of the back section of the shell; the first cavity and the third cavity are each provided with a sound absorption component, and unit cells of the sound absorption components are similar-triangle unit cells; and the side walls of the air inlet pipe and the internal insertion pipe are each provided with interference holes. Compared with a traditional Helmholtz silencer, the silencer of the structure can effectively reduce the structure complexity; and in addition, through the sound absorption components of the above structure, on the premise that sound absorption is achieved, airflow impact can be reduced, the maintaining frequency of the silencer is further decreased, and the using period is prolonged.