Aiming at the problem that the cable arrangement accuracy of the current cable arrangement methods for ocean winch is easily affected by environmental interference and contact friction and wear, the cable arrangement method is used by the non-contact visual detection method to measure the cable arrangement clearance which directly characterize the quality of the cable arrangement, and a subpixel measurement method for marine winch cable arrangement clearance based on improved Zernike moments is proposed in the paper. Firstly, the two-dimensional image gradient information is vertically projected into the one-dimensional waveform, and a vertical projection cable arrangement clearance location method based on Scharr gradient information is proposed to quickly locate the clearance area. Secondly, an improved sub-pixel edge detection method based on Zernike moments is developed by the main gradient direction interpolation to enhance the sub-pixel edge detection accuracy. Finally, a least-squares curve fitting method based on DBSCAN is used to fit multiple non-intersecting curves for measuring the cable arrangement clearance size. Experimental results show that the proposed method has higher accuracy and measurement precision by comparing with sub-pixel detection methods based on fitting method, interpolation method, and traditional Zernike moment, its measurement error is less than 0. 1 mm and relative error is less than 8. 60%, which provides a prerequisite guarantee for achieving accurate cable arrangement.