We propose an absolute distance measurement method that employs heterodyne and superheterodyne combined interferometers to achieve synchronous detection and demodulation of multiwavelengths. Coarse and fine synthetic wavelengths are generated by a dual-longitudinal-mode He–Ne laser and four acoustic optical frequency shifters. Further, to improve phase synchronization measurement for multiwavelengths, we analyze the demodulation characteristics of coarse and fine measurement signals and adopt a demodulation method suitable for both signals. Experimental results demonstrate that the proposed method can achieve high-precision synchronous demodulation of multiwavelengths, and standard deviation is 1.7 × 10^-5 m in a range of 2 m.