Abstract: In order to obtain the theoretical displacement, discharge pressure and power consumption when design the PC-type single screw compressor (SSC), the main geometric analysis of PC-type SSC has been carried out in this paper. By analyzing the intermeshing area formed by gate rotor tooth and groove of screw rotor and centroid distance, the mathematical models of groove volume and torque were presented for PC-type SSC. Analysis of a typical PC-type SSC with 117 mm diameter rotor shows that the calculated entire single groove volume has good consistency with that measured by 3D Pro/E software, with percentage error about 3.771%, the periodic variation of instantaneous torque is the same for different inlet pressure levels, the torque ratio, with its value close to 1, is independent of the inlet pressure of SSC and that the power consumption increases with increase of inlet pressure. Results from the established mathematical models of groove volume and torque is of great importance for engineers to design and manufacture the PC-type SSC.