To solve the precision machining problem in the structural surface mould manufacturing process, a new no-tool precision machining method based on softness abrasive flow machining (SAFM) is proposed. The key technology of SAFM is the characteristic analysis of two-phase flow. To solve this problem, a two-dimensional model of the two-phase flow is established by the topological structure transformation of level set method. This mechanics model is used to simulate the motion of the turbulent flow and work out the characteristic parameters of abrasive two-phase flow. The simulation results show that this model can preferably simulate the motion of the two-phase flow and calculate velocity and pressure with k- model and Preston equation. Therefore the feasibility of SAFM can be confirmed and a good reference can be provided for the further research.