The present invention discloses a RF measuring device with a phase fixation function. The device comprises a local oscillator module which outputs a local oscillator signal and a control module. The local oscillator module comprises a clock generation unit, an analog and digital mixed frequency synthesizer chip, a filtering unit and a voltage controlled oscillator. The clock generation unit outputs phase identification reference clock to the analog and digital mixed frequency synthesizer chip. The control module controls the frequency-division ratio of the analog and digital mixed frequency synthesizer chip through emitting a frequency-division control time sequence signal. The analog and digital mixed frequency synthesizer chip provides voltage-controlled voltage to the voltage controlled oscillator according to the frequency-division ratio, the phase identification reference clock and the feedback local oscillator signal. The filtering unit filters the high-frequency noise of the voltage controlled voltage. The voltage controlled oscillator outputs local oscillator signals with different frequencies according to the voltage controlled voltage. The clock generation unit outputs the phase identification reference clock to the control module and provides work clock to the control module. The control module carries out phase fixation on the phase identification reference clock and the frequency-division control time sequence signal, and the stray signal in the local oscillator signal is reduced.