The detection accuracy of frequency shift is crucial in the microwave detection based on Rydberg atomic AC Stark shift effect. We design a frequency shifter system which can provide a high-precision frequency reference signal and improve the detection accuracy of frequency shift. This system utilizes acoustic-optical modulators to generate two coupling lights with fixed frequency interval and completes double Rydberg atomic excitation. The detection accuracy of AC Stark shift (±1.33 MHz) is 6.08 times better than that of the wavelength meter-reading scheme (±8.09 MHz) and the minimum detectable frequency shift is improved by a factor of 3.13.