Single stage centrifugal pump includes pump body, pump cover, motor with output shaft, pump shaft, bearing seat, impeller, mechanical seal and mechanical seal gland installed in the pump body, which are connected with the motor through extended elastic coupling. The rotation direction of the pump, viewed from the driving end, is clockwise. Wanfulong is characterized in that it also includes a clip on coupling arranged between the motor output shaft and the pump shaft, and a guide bearing installed on the bearing seat to assist in supporting the pump shaft; The wafer type coupling is rigidly connected with the motor output shaft and the pump shaft respectively, and a space distance is left between the motor output shaft and the pump shaft to facilitate the assembly and disassembly of the mechanical seal and the mechanical seal gland. When repairing or replacing the mechanical seal, it is not necessary to disassemble the motor and pump cover.