Abstract: It is more and more important to determine the shear strength of rock-soil aggregate mixture quickly and accuratly while the mixture is widely used in roadbeds,dykes,dams and foundations.Lab large-scale direct shear tests are broadly adopted in engineering due to their obvious advantage,even though the test principle is slightly departure from the Mohr-Coulomb law.To avoid this problem,the authors improved the equipment of lab large-scale direct shear tests and developed a special new one which overcame the disadvantages of normal equipment,made the result more accurate and could be used to analyze the shear surface and dilatability of the mixture.