Abstract: The interaction of cracks with different locations and sizes is a key factor leading to the damage of rock. Based on the Kachanov method, the interaction rules between two offset parallel cracks with different level intervals, vertical intervals, crack lengths and crack angles are investigated by analyzing the stress intensity factor ratios under tension-shear stress and compression-shear stress. The compression tests on rock-like specimens with two unequal offset parallel cracks are performed, and the theoretical analysis is proved through the researches on the crack initiation and initial stress variation rules. The results shows that the offset parallel cracks exist reinforcing effect, shielding effect and null effect, and the three effects transform mutually along with the variations of level intervals, vertical intervals, crack lengths and angles. The reinforcing effect and shielding effect become more and more severe with the decrease of distance to the crack tip, and K_I changes greatly when the crack angle is 60°and K_II changes greatly when the crack angle is 30°.