Abstract: The finite element method was used to simulate the three dimensional thermal diffusion properties of woven carbon fiber/epoxy resin (CF/EP) composite. TexGen was used to create a 3D simulation model of 20-layer woven CF/EP composite. The effective volumetric specific heat and thermal conductivity of the porous matrix in samples with different thicknesses were calculated to set the material properties. The amplitude curve was used to simulate periodic laser point light source for finite element simulation. Taking a sample with a porosity of 0% as an example, non-linear fitting was used to solve the thermal diffusivity, and the optimal modulation frequency range was selected as 0.1-2 Hz. On this basis, samples with different thicknesses were studied to analyze the influence of porosity on the thermal properties and the anisotropy of thermal diffusion. The results show that the in-plane thermal diffusivity of the woven CF/EP composites decreases with the increase of porosity. When the porosity is less than 1.55%, the thermal diffusivity decreases by 5.4% as the porosity increases by 1%. When the porosity is greater than 1.55%, the rate of decline slows down, just as 2.4%. In the plane, the thermal diffusion rate along the weft yarn and warp yarn is faster, but along the 45° direction of the warp (weft) yarn is slower. While in the vertical direction, the thermal diffusion along the normal is the fastest due to the penetration of the point light source, which reflects the anisotropy of the thermal diffusion.