[Objective] The degree of damage to small leaf poplar (Populus simonii) by coal mining subsidence was studied in order to provide a theoretical basis for the later restoration of artificial forests. [Methods] Damages in the Lijiata mining area to P. simonii root systems at different cracks in different slope positions were observed and recorded. The relationships between root damage rate and damage types and slope position, crack types, dislocation differences, crack widths, and the horizontal distances from roots to cracks were analyzed by using mathematical statistical software in order to characterize damage characteristics of P. simonii root systems. [Results] ① The horizontal P. simonii root system was mainly distributed in 0—60 cm soil layer. The number of roots in 0—10 cm soil layer was the largest, accounting for 40.1%—43.2% of the root system, and the roots in 50—60 cm soil layer accounted for 0.63%—3.71% of the root system. The fraction of the root system gradually declined with increasing soil depth. ② Root damage was most serious on slopes. All types of root damage existed in the subsidence cracks and sliding cracks, with damage following the order of pull apart>skin crack>twist>pull out. There was no pull out damage in the sliding cracks, and damage followed the order of skin crack>twist>pull apart. Root damage in the subsidence cracks was most serious. ③ The number of damaged root systems decreased gradually as root diameter increased. Roots with diameters less than 2 mm were almost pulled apart, and roots with diameters less than 5 mm were mainly pulled apart. Roots with diameters bigger than 5 mm were dominated by skin cracks, and then were pulled apart. The thicker the root was, the less the pull apart occurred, and the more skin cracks were observed. When roots were bigger than 11 mm in diameter, the number of skin cracks increased rapidly. ④ The main factors causing root damage can be ranked from large to small as crack width, dislocating difference, and distance from root to crack. The wider the crack, the greater the dislocation difference was, and the more serious was the P. simonii root system damage. Smaller root crack distance resulted in greater amounts of root damage. When the root crack distance was less than 1 m, the root damage was most serious. [Conclusion] The degree of root damage under different types of soil cracks differed. Different treatment measures should be formulated for vegetation restoration suitable to different fracture types in coal mining subsidence areas.