Length measurement plays an important role in science and technology. From the three-dimensional coordinate measurement system of industrial manufacturing to the micro-scale and nano-scale microsystem, high-precision distance measurement plays a fundamental and crucial role. Due to the multiple characteristics of laser, such as high collimation and high coherence, laser ranging technology has been widely used in distance measurement. Some measurement methods based on frequency domain interferometry have been widely used in high-precision measurement. Compared with light wave, microwave can achieve more accurate frequency control and frequency measurement. A method called Optical Carrier-Based Microwave Interferometry (OCMI) has come out for high precision sensing. OCMI is similar to optical frequency domain interference. This method uses microwave modulated on broadband light, and then calculates the optical path difference with microwave phrase difference, therefore OCMI also has the advantage of high measurement accuracy. Because the frequency resolution of the microwave spectrometer is stronger than that of the spectrometer, the non-ambiguity distance of OCMI is greater than that of optical frequency domain interference. In addition, the broad-spectrum light acting as a carrier is not sensitive to transmission mode and dispersion OCMI can avoid the influence of inter-mode interference and polarization on ranging. OCMI has been widely used in fiber distributed sensing and fiber delay measurement. Taking the effective refractive index of the fiber as a constant, the length of the fiber can be calculated by the relationship between the length and the time delay.This paper proposes a ranging method based on optical carrier-based microwave interferometry. The microwave is modulated to broadband laser by electro-optic modulator. The Fiber Bragg Grating (FBG) reflects part of the carrier wavelength of microwave modulated light to realize the light splitting. The reflected light from FBG and the light reflected by the target are incoherently superimposed in the circulator. Due to the optical path difference between FBG and target, the microwave interference occurs after photoelectric conversion. The optical path difference is calculated by analyzing the frequency domain interference spectrum of microwave, and then the distance to be measured is obtained. In this paper, several sets of ranging experiments have been carried out to verify the feasibility of the method. This paper has carried out multiple sets of ranging experiments to verify the feasibility, the results show that a system stability of ±2.7 μm and accuracy of ±2.5 μm in 150~450 mm measurement range is achieved. The ranging system has high measurement stability and accuracy, which provides a new method for high-precision measurement.