Abstract: Based on the continuummechanics theory, amixedmodewas setup to investigate the valid elastic modulus of composites. An improved mixed-mode method was proposed, and the revised formula of calculating the valid elastic modulus of compositeswas given. The calculational results of the valid elasticmoduli of two composites show that the biggest error is 9% for the improved method and over23% for theVoightmode,l theReussmodel and theHalpain-Tsaimodified formula, and the difference between the calculational and experimental curves of the valid elastic moduli of the two composites is small for the improvedmethod and great for the threemodels.