Abstract: Initiation toughness and propagation toughness are two important material parameters used to describe crack state.In order to study the rock dynamic initiation toughness and propagation toughness of mode I crack under medium and low speed impacts, an experimental study was performed by using single cleavage semi-circle compression (SCSC) specimen and a drop weight testing system.The crack initiation time and the propagation characteristic were measured by strain gauges or crack propagation gauge (CPG).By using crack softening (CS) model and linear equation of state, numerical models were established by using finite difference AUTODYN code.The experimental-numerical method was used to determine crack initiation toughness and propagation toughness.The results show that:Under impact loads, crack propagation speed is not a constant; Propagation toughness is inversely proportional to the crack propagation speed for the Longchang green sandstone; Propagation toughness is a not independent material parameter, but is related to crack propagation speed.