Abstract: Based on the generalized self-consistent principle, the mechanical properties of syntactic foams under tensile loading were investigated by a four phase sphere model, and the possible damages happening in syntactic foams were analyzed. After degradation of the model, computational results show that the predicted strength values of foams agree with experimental results well. By analyzing the normal stress concentration coefficient of interface between microspheres and matrix and von Mises stress distribution of matrix, it is found that the mechanical behavior of microspheres is similar with flexible solid particles's as the wall of microspheres is very thin. With the increase in wall thickness of microspheres, the influence of microspheres on whole mechanical behavior of material accords with rigid solid particle's. Finally, through introducing the damage effect factors, prediction for the strength of the syntactic foams were studied and an effective method for prediction of strength was provided.