Single-screw compressor has attracted attentions from the scientific community due to its excellent performance. However, thermal deformations of the star wheel, screw, and casing substantially affect the clearance between the components, and hence reduce the performance of the single-screw compressor. In this study, the thermal deformation of a meshing pair of the single-screw compressor was investigated using a finite-element-based thermo-mechanical coupled model. This model was developed based on measured thermal boundary conditions during compressor operation. The effect of thermal deformation on the compressor sealing clearance was then studied. The results showed that the thermal deformation of the casing, screw, screw shaft, and star wheel significantly affected the clearance between the tooth tip and the groove bottom as well as the meshing pair clearance distribution. The change of clearance between the casing and screw is up to 0.03 mm while the change of the clearance between the star wheel tooth tip and screw groove is up to 0.05 mm. Furthermore, it was found that the spatial position meshing error caused by the thermal deformation was one of the major reasons for the wear of the meshing pair of the single-screw compressor. The simulated thermal deformation results agreed well with the experimental data. The clearances of the compressor were modified based on the thermal deformation in a single-screw compressor with a capacity of 6 m³/min and the results showed that the modified compressor can operate reliably. This indicated that the developed model could be used in the design of the single-screw compressor. It provides guidance for the design and optimization of large single-screw compressors.