The pulley is a small part of complex machine. Its lifetime and quality directly affect the reliability and safety of the entire equipment. Firstly, this paper introduces the design requirements for the main pulley of the oil rig HTC15J01 for analysing and calculating the stress and load distribution of the main pulley. Then, based on the design calculation in terms of stability, strength, and extruding strength etc. of the pulley, the key structural sizes of the main pulley were obtained. Finally, through checking calculations and finite element calculations in terms of stability, strength, and extruding strength etc., the analysis shows that the structure size parameters of main pulley meet the requirements of the oil rig. The calculation results of the HTC15J01 rig crane pulley provide a theoretical basis for the application of the pulley in the project.