The crack initiation and propagation process of hydraulic fracturing were reproduced using a coupled particle flow code (PFC) computational fluid dynamics (CFD) method in mixed ground. The breakdown pressure of mixed ground was investigated based on orthogonal test principles and five influencing factors were analysed. The crack propagation process in mixed ground was investigated under different normal bond strength ratios between hard and soft grounds and stress ratio. The minimum principal stress has the most influence on breakdown pressure, followed by stress ratio. Stress ratio was the determining factor for crack initiation direction. The result can be used in the engineering design of hydraulic fracturing projects.