The invention discloses a water-leaving quality change monitoring system device of freshwater fish, and a monitoring method thereof. The water-leaving quality change monitoring system device comprisesa water tank, a monitoring probe and a spray head, a water pump is arranged on one side of the water tank, a first bevel gear is engaged with a second bevel gear, and the first bevel gear and the second bevel gear are horizontally and vertically distributed respectively, a bottom end of the water tank is fixed to a top end of a power box, a horizontally distributed rotating shaft and a motor areinstalled in the power box, furthermore, the motor is connected with the rotating shaft, a second lateral cylinder is sheathed at the middle segment of the rotating shaft, the horizontally distributedsecond lateral cylinder is rotatably installed in the power box through a bearing seat, a horizontally distributed placement plate is slidably connected in the water tank, and a vertically distributed vertical column is fixed in the water tank. By adopting the water-leaving quality change monitoring system device of freshwater fish, and the monitoring method thereof, under the premise of ensuringthe original function efficiency of the device, structural equipment for automatically adjusting the water leaving environment is added inside the device, so that the overall function of the device is more perfect, and the monitoring data are more accurate.