The invention discloses a method and system for measuring the static amplification factor of a voltage control loop of a self-excitation excitation system. The method comprises a step of adjusting theworking condition of a generator such that the generator runs without a load at a rated speed, and starting excitation control, a step of ending integral and differential links in voltage control main loop proportional, integral, differential control PID parameters of a test generator set excitation system, setting a fixed magnification factor, changing the terminal voltage of a given generator according to a preset amount, and recording the terminal voltage, excitation voltage and excitation current of the generator, a step of calculating a commutation reactance coefficient of a thyristor rectifier bridge according to a no-load characteristic curve, the terminal voltage, the excitation current, calibration excitation system current and a voltage reference value of the generator, and a step of calculating a measured amplification factor according to a terminal voltage given value, a terminal voltage actual value, the excitation voltage, the excitation current, and the commutation reactance coefficient of the thyristor rectifier bridge, and obtaining and calculating the amplification factor of a thyristor.