The invention discloses a power supply system applied to a large-scale water transmission and distribution system. The power supply system comprises a first voltage conversion module, a second voltageconversion module, a first monitoring circuit and a second monitoring circuit; the input end of the first voltage conversion module is connected in parallel with the input end of the first monitoringcircuit and then is connected with a high-voltage transmission line; the first voltage conversion module is used for converting high-voltage power into a production working voltage; the input end ofthe second monitoring circuit is connected in parallel with the input end of the second voltage conversion module, and then is connected with the output end of the first voltage conversion module; thesecond voltage conversion module is used for converting the production working voltage into a production stop working voltage; the input end of the second voltage conversion module is also connectedwith a second disconnecting switch; and the second disconnecting switch is in T connection with a production working power source. With the power supply system applied to the large-scale water transmission and distribution system of the invention adopted, electric energy loss is effectively reduced; the service life of power supply equipment is prolonged; economic cost is effectively saved; and power supply modes are reasonably switched for production and production halt, so that unnecessary electric energy waste is avoided.