Plastic moldings were widely applied due to such merits as light weight and fine surface. The cylindrical blade can be easily casted by plastic injection molding process because of its simple surface boundaries. A new axial guide vane was designed along with the development of 125QJ20 plastic deep well pump. The blade of the axial guide vane is divided into two parts: the cylindrical section and the twisted section. Thus the molds can be freely removed during injection molding process. In order to examine its performance, a radial guide vane was designed with the in-house code DLSJ for guide vanes. Each guide vane was assembled with the same impeller, and the other components remain identical. The numerical simulations of internal flow field and external characteristic of the two models were carried out by the FLUENT software with the standard k-ɛ model and the SIMPLEC algorithm. The external characteristic comparison shows that under the rated condition, the efficiency of the pump installed with the axial guide vane is 8.9% higher than that of the radial one. In addition, the first one achieves a head increase of 1.5 m. The comparative analysis of the internal flow field of the two guide vanes reveals that the axial guide vane can effectively improve the internal flow pattern and obtain better hydraulic performance. Obviously, the molding process of the new axial guide vane is simple, which can effectively reduce the cost of mass production. Thus this design shows a promising market prospect for plastic deep well pumps.