Abstract: The Model Loop System studying the characteristics of wax deposition is presented. Some factors are considered, including the decrease of test tube wall temperature, the increase of viscosity and the aberration of flow field in the tube. A new method of calculating the thickness of wax deposition in the Model Loop System tests is put forward. The research on wax deposition properties of Qinghai crude oil is performed, and a plateau area of wax appearance at about 40℃ is found; if the tube wall temperature is higher than the wax appearance temperature or lower than solidifying point, no wax deposits. Molecular diffusion plays a significant role on the wax deposition on the inside tube wall while the shearing diffusion of wax particles plays little.