In photoelasticity,the experiment gives only the difference of principal stresses and their directions. In order to obtain three plane stress components,the supplementary equations are required. Using oblique incidence method one can obtain the three plane stress components. Considering the experimental data is not accurate,multi-angle oblique incidence established nonlinear overdetermined equations are used to calculate stress components. Conventional method for solving nonlinear overdetermined equations is difficult,new particle swarm optimization algorithms are proposed for oblique incidence stress separation. Demonstration of the method on disc under diametral compression is performed using computer simulation. The method is effective and simple for stress separation,providing whole field stress components.