The distribution of heat release (HR) is crucial for the formation of the thermal throat and the control of operational modes in the dual-mode scramjet. In this study, OpenFOAM was utilized to simulate the combustion of a dual-mode scramjet operating at Mach 6 with a low dynamic pressure of 30 kPa. A combustion efficiency statistical method was defined based on the HR distribution, and it was validated using simulation data. Under different injection strategies, differences in HR distribution characteristics and combustion performance were obtained. The research results indicate that using the gas mass-averaged parameters for calculating HR distribution achieves good accuracy, with an error of less than 3.3% compared to HR obtained through three-dimensional direct integration. Therefore, this method can accurately obtain the one-dimensional HR distribution and combustion efficiency of dual-mode scramjet. When using two-stage injection, the peak HR is lower, the length of the HR interval is greater, and the HR tail extends to the nozzle. In contrast, with single-stage injection, the peak HR is higher, and the HR is mainly concentrated in the area of the strut and cavity. When the global equivalence ratio (ER) is greater than 0.6, two-stage injection has higher combustion efficiency, while as the ER decreases, adopting a single-stage concentrated injection strategy can achieve a maximum 4.7% increase in combustion efficiency. And the difference of combustion efficiency under different ER is more than 10%. The conclusions of this study are beneficial for characterizing the HR distribution and combustion efficiency of the dual-mode scramjet, providing more efficient solutions for combustion organization of dual-mode scramjet.