The clearance fit mode between the stator and rotor is adopted for an all metal progressive cavity pump (PCP). Thelaws of the clearance leakage cannot be analyzed by referring to the methods of the traditional PCP in interference fit. Based on the leakage mechanisms between cavities inside the PCP in clearance fit, the leakage structure parameters are calculated accord- ing to the line contact lubrication theory, and then the Poiseuille - Couette leakage model is established with the application of clearance flow principles considering different leakage directions synthetically. By comparison between the model results and experimental laboratory data, the accuracy of the leakage model is verified. The results show that the displacement performance of an all metal PCP with a specific structure is mainly affected by Poiseuille leakage flow, and the effects of the Couette leakage flow is very small; With an increase in the working pressure difference and a decrease in the rotational speed and fluid viscosity, the effects of the clearance slippage on the pump displacement become more significant. An all metal PCP is more suitable for well production of viscous fluid. In actual field applications, better working performance can be assured by means of appropriate- ly adapting the pump stages and the rotational speed.