The invention discloses a flushing device for a factory trench, which comprises a flushing water pipe (3), a valve (4), infrared detection devices (1 and 2) and a power distribution device (6), wherein one end of the flushing water pipe (3) is connected with a process water main pipeline (5) through the valve (4), and the other end is communicated to the rearmost end of the factory trench; the infrared detection devices (1 and 2) are arranged in the factory trench (7) and transmit detected signals to the power distribution device (6); and the power distribution device (6) controls the openingand the closing of the valve (4) and controls the flushing process according to the signals. Because the flushing device is arranged on the process water main pipeline, by utilizing a circulating flushing water pipeline device, the invention can completely solve the problem of low efficiency for clearing slurry in the factory trench and reduce clearing and maintaining quantity of the factory trench.