The invention provides an assembly method of a low-noise water supply pump. The assembly method comprises the following steps of designing a shaft system precision decomposition process, roughly positioning and assembling a motor bracket and a support, measuring the coaxiality of the hole positions of the motor bracket and the support, repairing and matching the coaxiality of the hole positions of the motor bracket and the support, assembling a transmission shaft, a bearing and a bearing supporting seat, forming a shafting no-load precision test by the transmission shaft and the bearing, assembling a cylinder body, a piston and the transmission shaft, testing the precision after assembling, detecting and debugging the noise of a motor-free lower shaft system, combining and assembling a motor and a motor rubber mat, and combining and assembling a coupler and a coupler shock insulator. According to the assembly method, the problems that resonance is prone to being generated due to the fact that motor vibration reduction assembling control of the space low-noise water supply pump is not quantified, shaft system rotating friction noise is prone to being caused due to the fact that precision such as coaxiality is not high during shaft system assembling, the noise is out of tolerance due to the fact that noise and performance measuring process control is not refined and the like are solved, the performance and the service life of the water supply pump are improved, and long-term operation safety is ensured.