The invention discloses a water depth automatic tracking device in a non-steady flow simulation test, and the device comprises a sleeve, a water surface tracker, and a controller. The water surface tracker is located in the sleeve, and the interior of the sleeve is provided with a first LED, a second LED, a first photodiode, and a second photodiode. The first LED is arranged to be exactly opposite to the first photodiode, and the second LED is arranged to be exactly opposite to the second photodiode. The first and second photodiodes are respectively in signal connection with the controller, and the controller is connected with a first tracking motor and a second tracking motor. According to the invention, the water surface tracker depends on a floating force to move up and down along with a water surface, and then achieves the tracking of a corresponding water depth through the first and second tracking motors. The device control the starting of the tracking motors through the high sensitivity of the photodiodes and LEDs, and improves the tracking precision.