A dual time-step approach was developed for simulation of unsteady supersonic combustion flow. The flow and reaction were separately calculated with a time-splitting method. The flow equations were solved by the dual time-step approach with the inner iteration proceeded by a LU-SGS method. The source equations were solved by 2^ndorder trapezoidal formulas. The influences of the time-splitting scheme and the time step were studied. The results show that the 1st order time-splitting can slightly overestimate the chemical efficiency and a 2^ndorder time-splitting should be implemented. The time step has a significant effect on the results. In order to ensure the computational precision of the uncoupled method, the time step should be kept small enough so that the unsteady behaviors of the large scale vortices, which dominate the transport processes in the flow, can be captured accurately.