In this study, a series of computational fluid dynamics (CFD) simulations was conducted to evaluate and optimize the design of the internal flushing channel for a drill bit. The Star-CCM+ code was used to simulate the multi-phase flow of flushing air and escaping rock particles during drilling work. The values of the input parameters used for the simulation were obtained from in-situ drilling test results. Finally after choosing three major design factors and determining their appropriate sizes, the experimental design method known as response surface methodology (RSM) was used to obtain the optimum value of each factor.