To clarify the deflection and propagation mechanism of interface-controlled fractures during commingled hydraulic fracturing in coal-measure composite reservoirs, a fracture deflection criterion was established to investigate the effects of interface structure, interlayer property contrast, and in-situ stress conditions on fracture propagation behavior. Furthermore, numerical simulations were conducted to evaluate the feasibility of commingled hydraulic fracturing in typical composite reservoirs of the Qinshui Coalfield. The results show that when each parameter is in the range that can make the hydraulic fracture extend along the interface at the interlayer interface, the interface inclination angle and the difference in ground stress mainly affect the type Ⅰ and Ⅱ stress intensity factors at the tip of the fracture, and the difference in fracture toughness, the injection rate, and the viscosity of the fracturing fluid mainly affect the type I stress intensity factor at the tip of the fracture, which in turn changes the size of the fracture toughness of the fracture in the adjacent layers, and changes the extension paths. The bigger the difference in ground stress, the smaller the difference in fracture toughness, the more favorable it is for the fracture to be deflected along the interface. The larger the ground stress difference and the smaller the fracture toughness difference are, the more favorable the deflection of cracks along the interface is, and the extension distance of cracks along the interface is shorter when the interface angle is between 40° and 60°. The fluid injection rate and the viscosity of the fracturing fluid can be appropriately increased to promote the deflection of cracks along the interface, and the over-improvement is not only ineffective, but also will cause a waste of resources. Both the coal-series composite reservoir composed of the No.3 coal seam of the Shanxi Formation and its overlying roof, and the composite reservoir composed of the lower part of the No.14 coal seams of the Taiyuan Formation and its underlying floor in the Yushe-Wuxiang area of the Qinshui Basin are suitable for integrated hydraulic fracturing. The fracture extension distances along the interlayer interfaces can reach up to 6.25 m and 0.25 m, respectively. These findings provide a theoretical basis for optimizing fracturing methods and engineering parameters for the efficient development of coal-series composite reservoirs.