FLAC3D strength reduction method had been adopted to research on the stability of 3D slopes with interbedding of soft and hard rocks, when the dip angle of stratum and the angle between the strike direction of slope and stratum changed, and the failure modes were identified and analyzed. The results show that:to identify the failure modes of slopes, the angle of the rock stratum, the angle between the strike direction of slope and stratum and the cut off condition on the slope surface should be considered. When β (the intersecting angle between the strike direction of slope and that of strata)<90°, with the increase of α (the strata inclination), the failure modes change from creeping-pressure induced ripping, plastic flowing-ripping, sliding-ripping to sliding-bending and bending-ripping; when β>90°, the failure modes change from plastic flowing-ripping to sliding-bending, and then become bending-ripping. With the increase of the angle between the strike direction of slope and stratum, the slope stability coefficient increases at first and then decreases, it reaches the maximum when β=90°, and the greater the α is, the greater the coefficient peak is. For the dip slope, with the increase of the angle of stratum, the trend of failure modes is:creeping-pressure induced ripping, sliding-ripping, sliding-bending, and bending-ripping. The stability coefficient decreases first and then increases, and there is a most unfavorable angle of the stratum, the corresponding stability coefficient is the least. As for the anti-dip slope, the trend of failure modes is creeping-pressure induced ripping and bending-ripping, and the stability coefficient increases gradually.