After machining metallic parts, there will be residual stresses generated by machining in surface layers of the machined parts, the deformations caused by surface residual stresses have a strong effect to the parts accuracy. In order to predict the deformations caused by surface residual stresses generated by milling Ti6Al4V parts, this paper presents a method for measuring the equivalent surface residual stresses and the effective depth to solve this problem. The material in the surface opposite to the machined surface were removed twice, the depth and the neutral layer of the workpiece were changed, the change of the bending deflections and the strains measured from the machined surface were measured after that, and then the equivalent surface residual stresses and the effective depth can be calculated out. FEA (finite element analysis) was used to validated the correctness of this method, the results calculated by FEA correspond well to those measured in the experiments, so it can be concluded that the results got from the method proposed in this paper are correct, they can be used to evaluated the surface residual stresses generated by milling and predicted the deformations caused by surface residual stresses, as to predict if the parts accuracy can meet the requirement.