Conglomerate reservoir is an important type of unconventional oil and gas reservoir. During the development process, it is found that the nature of the cementation surface between the gravel and the matrix affects the fracture propagation behavior. In order to clarify the effect of cementation strength on crack growth, a numerical model of conglomerate uniaxial compression was established by using PFC2D discrete element package, and four stages of crack growth and micro-fracture mechanism were studied. The results show that the mechanical properties of conglomerate gradually change from plastic to brittle with the increase of cementation strength, and the critical cementation strength ratio is 0.3. The influence of cementation strength on crack growth is mainly in the elastic stage and the stable crack growth stage. Under weak cementation (CSR<0.3), isolated shear cracks occur on the gravel edges in the elastic stage, and shear crack networks are connected in the stable growth stage. Under strong cementation (CSR>0.3), there are almost no cracks in the elastic stage of the gravel edge, and only sporadic isolated tensile cracks in the stable crack growth stage. The additional stress caused by the disharmony of deformation between gravel and matrix under weak cementation is the reason that the edge of gravel is the first to break and form an isolated fracture. These results indicate that weak cementation is conducive to the formation of complex fracture networks. A reference is provided for revealing the fracture propagation law of conglomerate reservoir.