Variable speed rotary compressors are now increasingly favored in the market of household air-conditioners in China due to its advantage of energy saving and system stability. Oil supply system plays a pivotal role in high efficiency and good reliability of a variable speed rotary compressor. This paper presents an investigation of the effect of inlet structures on the performance of oil supply system of a variable speed rotary compressor by means of numerical simulation and experiment. The method of volume of fluid (VOF) has been employed in the simulation model and a novel experimental test rig is designed to perform oil flow rate measurements in order to validate the simulated results. With the help of numerical simulation, oil flow patterns in oil pump can be visualized and oil supply rate under different working conditions can be predicted. Good agreement between the simulated oil flow rates and the experimental data has been achieved. The results indicate that oil supply rate increases with an increase in oil level height, oil viscosity as well as the rotating speed. Vertical oil suction pipe with a tapered port contributes to oil pumping in comparison with a straight suction pipe and no suction pipe. Additionally, the minimum rotational speed at which oil starts to flow out of the oil pump increases with the oil inlet diameter and the increment of oil inlet diameter allows the improvement oil pumping performance at a high rotating speed.