Through the four-point bending experiment, using CCD camera as the observation means and the digital scattering correlation method, a group of composite rock specimens composed of fine sandstones with different strengths are experimentally investigated to analyze the influence law of interlayer slip on the damage of composite rocks. The results show that: (1) Multiple load peaks and sudden drops occur during the damage of composite rock, which are related to the generation of cracks, and when cracks are generated in one layer of the rock specimen, the stored energy is released synchronously, which leads to a sudden drop in the load curve. (2) Rock cracks appear in the vertical direction as a result of the joint action of pressure bending and interlayer slip, two-point loading in the four-point bending experiment provides vertical pressure, and interlayer slip provides horizontal friction, resulting in a shift in the location of the maximum horizontal strain, which is about 10 mm upward at the bottom of the rock. (3) The location of the composite rock cracks appearing in the horizontal direction is controlled mainly by interlayer slip and supplemented by pressurized bending. When analyzing the interlayer slip of the composite rock, it is found that the location of interlayer slip and the cracks are highly coincident, and the slip occurs first and then the cracks are generated. The above research results are important reference value for the study of the damage law of composite rocks.