Abstract: In order to study the developing law of sliding ground fissures caused by underground mining in the western loess hilly mining area of China,the definition and basic features of sliding ground fissures were given firstly in this pa- per. The dynamic developing model,gully gradient model,and gully position model were established using the UDEC numerical simulation software. Then,the dynamic developing law of sliding ground fissures was analyzed,the relation- ship between sliding ground fissures and gully was studied,and the reliability of models was validated through the en- gineering example at the 52304 working face in Daliuta Coal Mine,China. The results show that:① The development of sliding ground fissures could be divided into four periods,such as the accumulation period,the formation period,the dynamic developing period,and the stabilization period. ② The relationship between sliding fissure angle and gully gradient was the quadratic polynomial equation,and the relationship between sliding fissure angle and gully position was the linear equation. ③ The engineering example showed that the maximum relative error between the calculated values and the measured values of sliding ground fusser angle is 3. 4% ,which proves the prediction on the position of sliding ground fissure using this model is feasible.