The generating mechanisms of the main errors and noises of resonaor fiber optica gyroscope (RFOG) are analyzed, and the analyzing models are established. Combining with specific gyroscope parameters, the equivalent angular velocities of the errors and noises are estimated, and the relevant restraint measures are quantified. Taking bias stability of 0.1°/h in the RFOG as an example, to suppress the backscattering noise and the back reflection error, the requirement of the carrier suppression level should be as high as 112dB, and to suppress the Kerr effect, the light intensity difference between CW and CCW should be controlled at 3.86nW or less. The gyro bias stability caused by the uncertainty of the earth magnetic field direction is about 0.7°/h.