Abstract: In order to get the oil-gas-water equilibrium system of hydrocracking reaction effluent, a three-phase flash distillation module was established by HYSYS process simulation software combined with mass conservation principle. The impact of sulfur, nitrogen and chlorine contents in feed, amount of water injection and pressure on the deposition temperatures of NH4Cl and NH4HS in air cooler of reaction effluent (REAC) system were analyzed through the flash distillation module calculation. Results showed that the deposition of NH4Cl and NH4HS occurred mainly at the inlet and outlet of REAC system, respectively. The NH4Cl deposition temperature was greatly affected by the chlorine content of feed, thus, strengthening the dechlorination process of crude oil, setting the water injection point above the site of NH4Cl deposition and keeping 25% of liquid water in effluent could effectively reduce the risk of forming NH4Cl deposit. Sulfur content in the system and the amount of water injection were the main causes affecting the deposition temperature of NH4HS, enhancing desulfurization of recycle hydrogen and increase water injection to keep NH4HS deposition temperature below the operation temperature could avoid happening NH4HS deposition significantly.