An approach to predicting the elastic property in warp direction of 2.5D woven composites is developed based on the energy equivalence principle. When the 2.5D woven composites are loaded in the warp direction, the deformation energy of the yarns and the matrix is analyzed. Then the prediction method for the elastic property in warp direction of 2.5D woven composites is conducted by the equality relation between deformation energies of components and composites. Compared with the experimental data, the prediction results of the energy method are better than that of the volume average method, which proves the effectiveness of the method. It is also found that the parameter used in the method is easy to conduct.