Abstract: Eleven working points test and external characteristics test were taken for underground explosion-proof diesel before and after installing cooling and purified water tank. Some indexes of explosion-proof diesel were obtained under different conditions, including temperature of exhaust port, contents of waste gas and particulate matter, output torque, output power and fuel consumption rate. Influence of cooling and purified water tank on discharge, power and economy performance of explosion-proof diesel was summarized. The test results show that cooling effect for exhausting gas is obviously improved after installing cooling and purified water tank, and temperature of waste gas is lower than 50 °C. NOx exhaustion is greatly improved with the largest decreasing amplitude of 39.3%. CO exhaustion increases under the heavy load condition with the largest increasing amplitude of 22.2%. HC exhaustion has little variety. Particulate matter exhaustion increases a little under the heavy load condition. Power performance of the explosion-proof diesel decreases, and output torque and output power decreases 2.5% separately under the maximum torque condition. Economical performance decreases, and fuel consumption rate increases 3.2% at most.