The invention discloses a power supply method of a cold-state function test in a nuclear power plant. The power supply method comprises the steps of: sequentially operating three main pumps respectively used for heating a loop and circulating loop fluid, carrying out load limit on equipment positioned on the same line of inlet wires; when an auxiliary power supply loses power, automatically starting diesel engines on one line of inlet wires to drive upper charging pumps, equipment cooling water systems, important factory water utilization systems and residual heat removal systems on the corresponding lines of inlet wires, supplying power for an uninterrupted power supply on the same line of inlet wires and an uninterrupted power supply on another line of inlet wires through patches by the diesel engines so as to supply power for instrument control equipment, wherein the upper charging pump I is arranged on the A line of inlet wires, and the upper charging pump II and the upper charging pump III are arranged on the B line of inlet wires. By implementing the technical scheme of the invention, under the condition that a main power supply is unusable, the progress of building a nuclear power project is not influenced largely, and safety of tests and equipment is ensured.