The performance of twin-screw pumps that are widely used in industry hinges upon a number of factors. In this research, a systematic approach is presented, encompassing the design optimization of a Type-A screw and the subsequent performance evaluation of a twin-screw pump. We first investigate the effect of involute meshing angle on the contact line properties of the Type-A screw, and carry out design optimization. We then formulate a flow field analysis of the twin-screw pump using the screw tooth profiles and spiral surfaces under the optimal involute angles obtained, and analyze the pressure field, velocity field and other characteristics of the pump. The influence of contact line on the pump sealing property is also assessed. Concurrent with the numerical study, experimental investigation is performed to evaluate the rotating speed and power of the pump, as well as their intrinsic relations with the flow, pressure and power of the screws. These studies reveal that under the optimal design of the screw, the pump performance can be significantly improved. The methodology of design and analysis outlined in this research can be applied to other screw pumps, and the results of parametric analysis involved can shed lights on the development of screw pumps in general.