Laser Doppler measurement technology is a non-contact measurement method characterized by high measurement accuracy, high resolution, and rapid response. Currently, Self-developed laser Doppler length measuring instruments are still relatively few in China. The measurement errors ranging is from 0.5% to 1% in general which can not meet the requirement of cable manufacturing industry(0.3%). In contrast, the measurement errors of mature foreign products, such as the SL-type laser Doppler velocity and length meters developed by Proton Corporation in the UK and the uSpeed series laser Doppler velocity and length meters produced by Elovis in Germany, can reach 0.05%. Therefore, a high-precision laser Doppler length measurement with measurement error better than 0.05% is developed in this paper.First, optical frequency shifting technology is introduced based on an acoustic optical modulator(Fig.1). So, the base signal can be effectively filtered out combined with a high-pass filter. Then, an adaptive sampling algorithm is introduced(Fig.3) to further reduce system errors and enhance measurement accuracy at low speed measurement time. Therewith, Zoom-FFT spectrum thining algorithm is introduced (Fig.5) for dense spectral thining processing and energy centrobaric correction algorithm is introduced for spectral correction. The simulation analysis is carried out(Fig.6-Fig.8). Finally, an experimental system is set up, then accuracy and stability are analyzed(Fig.11).The accuracy of the adaptive sampling algorithm is analysed by simulations, and the relative errors at each speeds are plotted (Fig.6). The relative errors using the adaptive sampling frequency algorithm are generally lower than those with a fixed sampling frequency, particularly in the low-frequency region (corresponding to the low-speed phase). The impact of the energy centrobaric correction algorithm on Doppler frequency extraction accuracy are verified with 25 Doppler frequencies (Fig.7) . The frequency values directly output by the FFT is significantly inferior to energy centrobaric correction algorithm. So, the energy centrobaric correction algorithm can significantly improve the accuracy of Doppler frequency extraction. The relative error of Doppler frequency extraction is compared by using two methods(Fig.8). Simulation results demonstrate that the combination of the Zoom-FFT spectrum thining algorithm and the energy centrobaric correction algorithm can significantly reduce the relative error in Doppler frequency extraction and can enhance stability and accuracy. Comparison of the system's measurement results with calibration results (Tab.2) indicates that maximum measurement error and an average measurement error fully meet design objective (measurement error below 0.05%). Finally, the system's stability is analyzed by multiple repeated measurements with a speed of 1 m/s. The system's length measurement results indicates errors below 0.05% compared to the standard values (Fig.11).A high-precision online laser Doppler cable length measurement system based on a dual-beam dual-scattering optical path is designed. Optical frequency shifting in combination with a high-pass filter have effectively filtered out the base signal. The signal-to-noise ratio is improved significantly. The problem of low accuracy during low-speed measurements is solved by introduction of an adaptive sampling algorithm addresses. A higher-precision Doppler frequency has been extracted by combination of Zoom-FFT spectral thining algorithm and the energy centrobaric correction algorithm. The experiment results show that measurement accuracy achieve an accuracy of 0.05% with excellent operational stability.