A computational fluid dynamic (CFD) model and a deposition model are coupled to predict the molten slag deposition behavior in radiant syngas cooler (RSC) for entrained flow coal gasification. The slag particle deposition model is developed by identifying the excess rebound energy as a criterion to determine if the particle is deposited or rebounded from the wall while slag solidification in the impact process is also considered. The simulation results show that molten slag particles stick on the membrane wall between the height of 12.2-22.0 m for Reference Case with the maximum deposition rate 1.5 x 10(-5) kg/(m(2).s) at the position of height about 16.8 m. The deposition rate increases with increasing inlet temperature and operating load. Small inlet diameter leads to high deposition rate due to high transport rate and high deposit propensity, while small inner cylinder diameter leads to higher deposition rate due to higher deposit propensity.