Abstract: Aiming at the numerical issue at the interface during multiphase flow simulation with high density ratio and resulting unreasonable effect of convective motion, an implicit pressure algorithm based on volumetric flux free condition is proposed. Firstly, the causes of density approximation errors in the traditional multiphase flow simulation methods are analyzed. Secondly, the correlation calculation of "volume-compression ratio" is proposed to construct the linear relationship between fluid compression state and pressure. Thirdly, the constant volume solver and the volume flux free solver are designed respectively to realize the incompressibility of fluid volume and the divergence free of velocity field. In order to verify the performance of the proposed algorithm, the advanced fluid simulation method DFSPH is taken as comparison. And the rationality of simulation effect, numerical stability and convergence are taken as the qualitative and quantitative evaluation factors respectively. Experiments such as two-phase dam break and thermal convection are carried out under multiphase flow condition. The results show that the proposed method can achieve efficient and stable multiphase flow interaction. Under the same multiphase flow conditions, it can consume less calculation time and achieve convergence faster than DFSPH. It has good robustness, effectiveness and scalability in various complex simulation scenarios, especially suitable for simulating fluids with high density ratio.