In order to study the strength property of graphene modified soil, the graphene is uniformly mixed in the soil for direct shear tests under the control of dry density, and the scanning electron microscopy(SEM) is used to observe the structure of shearing surface of soil samples.Graphene was put into soil samples with the dosage of 0%, 1%, 2%, 3% and 4%, the water contents are 14%, 16% and 18%.The results show that the graphene can improve the failure strength of the soil, and no optimum dosage is found in this test.The cohesion increases with the increase of the graphene dosage, and decreases with the increase of water content, but the internal friction angle is almost constant.With the help of SEM, the mechanism of the modification of graphene in soil is analyzed from the micro level. The incorporation of graphene can fill the soil pores and improve the friction between the soil particles, it can enhance the shear strength of the soil.