In order to explore the comprehensive utilization technology of coal slime and other inferior coal in large coal-fired units and deeply understand the slime drying characteristics and application effect of steam tube rotary dryer slime drying system in ultra supercritical coal-fired units，the laboratory static tests and industrial tests were carried out. Under the static condition of 150-200 ℃，the 50-150 mm large particle size slime was dried at constant temperature. The relationship between slime particle size and drying time was analyzed. The industrial test was carried out by using a new steam rotary tube dryer-coal slime drying system(with a feed rate of 25 t/h）installed firstly in an ultra-supercritical coal-fired unit. The important indexes such as thermal efficiency and energy consumption of the system were analyzed. The results show that in the laboratory static test，it takes more than 50 min for the moisture content of coal slime mass(150 mm）decreasing from 24% to 15%. The coal slime mass drying process experiences two stages：preheating and rapid drying stage(＜10 min)，stable drying stage. With the increase of drying temperature，the period of preheating and rapid drying stage is shortened. In the industrial test，the drying time of coal slime was slightly shorter than the laboratory results under similar conditions，due to the depolymerization of coal slime in the dryer. With the increase of feed quantity，the moisture content of coal slime products increases. When it exceeds 17%，the system is prone to plugging. When the steam source pressure is 0.35-0.80 MPa，the inlet steam temperature should be reduced to less than 195 ℃，which is beneficial to coal slime drying. In addition，the thermal efficiency of the system can reach 58.6% under the condition of test operation，and it requires 0.112 t of steam and 3.94 kWh of electricity to produce 1 t of coal slime averagely.