The high-water holding capacity of coal gasification fine slag seriously affects its resource utilization. In this paper, the basic reason of the high-water holding capacity (64.64%) of coal gasification fine slag was clarified by studying the apparent morphology (SEM), the distribution of main elements (EDS) and pore structure (BET). Subsequently, through constant temperature drying experiments at different temperatures, the drying kinetics of coal gasification fine slag in constant temperature drying process was studied, and the logarithmic constant temperature drying kinetic model at various drying temperatures was established. Additionally, the drying temperature is from 80 to 120 ℃, and the equivalent moisture diffusion coefficient De of the sample during constant temperature drying is between 0.0025 and 0.0048. The higher the temperature, the greater the De value, the easier the moisture diffuses from the inside of the particles to the outside, and the easier the drying.