In view of the shortcomings of traditional testing methods in characterizing the compressive mechanical properties of composite materials, an innovative evaluation method based on the unidirectional properties of orthoclinometric laminates is proposed. Based on the three basic assumptions of the classical laminate theory (straight normal assumption, normal length invariant assumption and small deformation assumption), the stress-strain relationship of the laminate is established, and the analytical expression of the back-out factor is derived, so that the unidirectional mechanical properties of the composite materials can be obtained by the orthogonal laminate plywood test. Comparative tests show that the proposed method has higher accuracy and stability than the traditional tests, which verifies the applicability and effectiveness of the theory. The results show that this method can effectively evaluate the unidirectional compressive mechanical properties of high-performance composites, which has important engineering value.