In order to solve the problem that the accuracy of scale factor measurement of Resonance Fiber Optic Gyroscope (RFOG) is limited by the performance of turntable, a new method based on sawtooth equivalent input was proposed. By adding sawtooth wave to the RFOG's phase modulator, which works as equivalent input angular velocity, the RFOG closed-loop transfer functions under turntable input and equivalent input were analyzed, relationship between the parameter of sawtooth and equivalent input angular velocity was given, the scale factor and non-linearity were obtained by the scale factor test system. The scale factor is basically identical to the test result on the turntable, and the non-linearity is also improved from 0.42% to 0.26%. The test results demostrate that the scale factor test system based on sawtooth equivalent input can accurately measure the scale factor of RFOG, and effectively eliminate the measurement errors due to the vibration and imperfect precision of the turntable.