Recently, the turbo molecular pump that has the ability to pump a large quantity of gas under a low vacuum is required in the field of semiconductor and liquid-crystal device manufacturing. In this study, we propose the method of performance prediction for the turbine blade under a low vacuum, which enables the high throughput pump to be designed. The performance was analyzed by Stokes equation, which govern the low vacuum flow between the turbine blades in small Reynolds number. Experiments were carried out by conventional and optimized blade pumps under a low vacuum, and throughputs were measured. The comparison between the measurements and the predicted values shows that the present method predicts the performance of the turbo molecular pump in the pressure range of under 10 Pa with a sufficient accuracy for practical applications.