Slag cooler is an important auxiliary machine of CFB (circulating fluidized bed) boiler, its heat transfer efficiency plays an important role in the continuous and stable operation of CFB boiler, in order to further analyze the relationship between particle heat transfer efficiency. Based on the discrete element method and its numerical model, the heat transfer process of high temperature ash particles in the cold slag tube was simulated and analyzed by using the commercial software EDEM. The particle temperature T is normalized to dimensional temperature T*, and the effects of roller speed and particle diameter on the heat transfer process of ash particles are quantitatively analyzed by taking the average temperature, temperature probability density function T-PDF and particle motion law as indexes. Among them, the side length of hexagonal cold slag tube is 200 mm, the length is 500 mm, the wall thickness is 10 mm, the initial temperature of tube is 360 K, and the initial temperature of particle is 1200 K. The results show that the heat transfer efficiency of particles increases with the increase of rotating speed, and the heat transfer efficiency of n=10 r/min is 61.1% higher than that of n=4 r/min; The heat transfer efficiency of particles decreases with the increase of particle size. The heat transfer efficiency of d = 5 mm is 30.7% lower than that of d = 3 mm. The rotational speed affects the heat transfer efficiency by the number of turns, and the particle size affects the heat transfer efficiency by the number of collisions at the contact point.