In order to research the interaction rules of multiple cracks in coal and rock mass, based on Kachanov method, the interaction rules of two unequal offset parallel cracks with different level interval, vertical interval and crack length were analyzed by stress intensity factor ratio under tension-shear stress. The processes of crack initiation and propagation were simulated by RFPA2D, and the simulation results fit the theory well. The results show that the interactions of offset parallel cracks include exist reinforcing effect and shielding effect, and the two effects transform mutually with the variations of level interval, vertical interval and crack length; The reinforcing effect becomes more and more severe with the decrease of distance to the crack tip, and the rate of change becomes faster too. The shielding effect becomes more and more severe with the decrease of distance to the center of crack, and the rate of change becomes faster too. The influence range of crack becomes more and more wide with the increase of length.