Abstract: Microwave power frequency shift is an important factor for the rubidium atomic frequency standards’ stability. The mechanism of microwave power frequency shift was studied. Experiments were developed to improve the equality of the C field, light field and microwave field for reducing the coefficient of microwave power frequency shift. The mechanism of microwave power frequency shift was validated and the major characteristic of microwave power frequency shift for rubidium atomic frequency standards was induced through the experiment of microwave power frequency shift. The results show that the coefficient of microwave power frequency shift is less than 3.5×10^-12dB^-1 without the attenuation of signal-to-noise.