Abrasive water jets were selected to solve the problem of derusting of singlelayer oil tanks, which will be reformed into double-layer tanks. The effect of mixed abrasive water jet on the rust removal of inner wall of oil tank were evaluated by using computational fluid dynamics(CFD). By evaluating the maximum shear stress and the erosion rate of the jet impact target surface, the results show that the pressure of pre-mixed abrasive water jet is lower than that of the post-mixed when they perform the same rust removal effect. When the jet pressure is 20 MPa,the rust removal effect is most effective. The distribution of shear stress has a core area on the target surface, and the maximum shear stress is not at the center of the target surface. The erosion rate increases with the increase of the volume concentration of abrasive, the abrasive particle size, and the abrasive density, while the maximum wall shear stress does not change with it.