The invention provides a small and medium-sized hydropower station noise reduction system. The small and medium-sized hydropower station noise reduction system comprises a first noise reduction mechanism which is used for conducting noise reduction on the interior of a hydropower station, a second noise reduction mechanism which is used for reducing impact noise of downstream waterflow of the hydropower station, a third noise reduction mechanism which is arranged on the downstream portion of the hydropower station and matched with the second noise reduction mechanism, a monitoring mechanism which is used for monitoring the noise, and a control mechanism which is used for controlling the first noise reduction mechanism, the second noise reduction mechanism, the third noise reduction mechanism and the monitoring mechanism. Through the small and medium-sized hydropower station noise reduction system, noise generated by equipment in a hydropower station equipment chamber, noise generated during flood discharge, and noise generated when discharged flood impacts the river bed can be reduced, and the influence of the noise on personnel and surrounding residents in the hydropower station operation process is reduced.