On the issues of the effect of thermal loading on tensile properties of 3 D four一directional braidedcomposites，the finite element method of steady state thermal conduction analysis is derived based on the mesoscopis geometry model. The mechanical model of thermo-mechanical coupling behaviors analysis for 3 D four-directionalbraided composites is developed. By applying the thermal loads and the mechanical loads，the tensile strength of3 D braided four-directional composites are analyzed. The numerical calculations of the helix geometry model agreewell with the experiment data and this indicated that the present model can compute the longitudinal tensile strengthof 3 D braided composites effectively. The results indicate that theboundary heat flux has obvious influence on thethermo-mechanical strength of 3 D braided composites and lays a foundation for the follow-up transient state thermalconduction analysis.