The invention discloses a secondary water supply vector modulation unit with a drinking water purification function. The secondary water supply vector modulation unit mainly comprises a no-negative-pressure pipe network pressure-superposed steady-flow compensation device, a booster pump, an ultrafiltration membrane purification treatment device, a water purification tank, an ultraviolet ray disinfection device, a centrifugal pump, a speed regulation permanent-magnet three-phase synchronous motor, a control cabinet and a PC monitoring cabinet, wherein the ultrafiltration membrane purification treatment device is used for filtering microbes, bacteria, iron rust and other pollutants in water for water purification; and the speed regulation permanent-magnet three-phase synchronous motor is a special permanent-magnet motor for the centrifugal pump with variable frequency and speed regulation control, an NdFeB permanent magnet material is embedded into the permanent-magnet motor, and the speed regulation permanent-magnet three-phase synchronous motor can be directly used for driving the centrifugal pump to work in a 50 Hz three-phase AC environment. The secondary water supply vector modulation unit has the benefits that water purification and guarantee functions are achieved; energy, water and land saving are achieved through no-negative-pressure pipe network pressure superposition; the speed regulation permanent-magnet three-phase synchronous motor is arranged to drive the centrifugal pump to conduct variable-frequency water supply, so that the energy-saving effect is further improved; a relatively wide economical operation range is realized; the operation is reliable; and the service life is long.