The invention discloses a silencer of a motorcycle cylinder. The silencer comprises an air inlet pipe, wherein the air inlet pipe is connected with one end of a sound absorption and air inlet opening through threads; the other end of the sound absorption and air inlet opening penetrates through a shell and is fixedly connected with a sound absorption chamber; the left side of the sound absorption chamber is fixedly connected with one end of a sound absorption and air outlet opening; the other end of the sound absorption and air outlet opening is connected with an inner pipe through threads; the inner pipe penetrates through an outer pipe, and extends into the outer pipe; sound attenuation holes are formed in the inner pipe; the top and the bottom of the inner pipe are separately fixedly connected with a sucking disc; each sucking disc is fixedly connected with the inner wall of the outer pipe; the left side of the outer pipe is fixedly connected with one end of an air outlet; and the other end of the air outlet penetrates through the shell, and is connected with an air outlet pipe through threads. According to the silencer of the motorcycle cylinder, a double-sound-attenuation structure is adopted, so that a sound attenuation effect is more obvious; use by people is facilitated; and a driver is free from annoyance caused by noise.