The mode-cleanerconsisting of a ring cavity with three mirrors was designed based on the theoreticalanalyses and experimental measurements to the intensity noise spectra of anall-solid-state laser. The intensity noise of a homemade single-frequency Nd:YVO4 laser has beensignificantly decreased by using the mode-cleaner with the characteristic of filteringhigh frequency noise. The noise frequency to reach the shot-noise-limit has been reducedto 7 MHz from 30 MHz without the mode-cleaner. In design, the requirements of both narrowbandwidth and higher transitivity for the cavity were considered compatibly. Thetransitivity of mode-cleaner is 70%.