［Objectives］In order to investigate the effect of water spray on the soot removal of diesel engine flue gas, relevant experiments were carried out. [Methods] Dekati Low Pressure Impactor (DLPI) was used to sample the smoke black in the flue. The heating belt was wrapped on the sampling gun and the temperature was controlled to prevent the condensation of wet flue gas after spraying, and to maintain the same state of soot in the flue. Firstly, the uniformity of flue gas concentration was measured by the flue gas analyzer to verify that the flue gas distribution was basically uniform, and the sampling time was determined by DLPI. Then, the soot purification efficiency under different diesel engine load and different spray water volume was measured and compared. [Results]The results show that the efficiency of soot removal can reach 50%. Under the same spray rate, the soot removal efficiency of diesel engine under 100% load is higher than that under 50% load. When the spray rate reaches a certain value, the efficiency of soot collection and purification may reach the extreme value. Under 50% load, the contact time between water mist and soot is longer, and the agglomeration effect of small particles is more obvious than that under 100% load. [Conclusions]The measurement results show that the water spray can effectively reduce the soot emission of diesel engine.