The present invention discloses a high-capacity phase modifier test method with small power grid influence. The phase modulation test of a phase modifier is performed in the condition that two phase modifiers with the same bus are running at the same time, one of the phase modifiers performs a leading phase operation test while the other one thereof performs a phase lag test, and the phase modifier of the leading phase operation test provides a power grid environment with low power grid voltage for the phase modifier of the phase lag test, and at the same time, the phase modifier of the phase lag test provides a power grid environment with high power grid voltage for the phase modifier of the leading phase operation test, so that the problem is avoided that the voltage at the terminal of the phase modifier reaches the lower limit caused by not high enough power grid voltage in the leasing phase operation test or the problem is avoided that the voltage at the terminal of the phase modifier reaches the upper limit caused by not low enough power grid voltage in the phase lag operation test. The high-capacity phase modifier test method with small power grid influence is able to allow a phase modifier to obtain proper phase modulation performance through a test and reduce the influence on power grid voltage to a certain extent at a test, and a good application prospect.