3D braided composites have been widely used in aerospace engineering and thermal conductivity is one of its important physical properties. Based on the mesoscopic unit cell of 3D 4-directional braided composites, the macro- and micro- multi-scale models for predicting thermal properties of 3D braided composites are established, including the homogenization model for the equivalent properties and multi-scale model for the temperature distribution. And the equivalent properties are calculated by the multiscale finite element algorithm, and agree well with the experimental results. The influences of the braiding angle and fiber volume fraction on the thermal conductivity coefficient are also studied. In addition, the distributions of temperature field inside composites are determined, providing a basis for the analysis of the thermo-mechanical coupling