Abstract: To address the industrial demand for high-precision and rapid measurement of the spherical radius of differential planetary gear tooth surfaces, a non-contact measurement method based on point cloud processing is proposed.Firstly, the point cloud data of the planetary gear is preprocessed and the point cloud of tooth surface is extracted. Secondly, spatial cutting planes are generated at specific locations, rotational sampling of the tooth surface point cloud is performed, and the contour points on the intersection line between the tooth surface and the spatial tangent plane are extracted after each sampling. Thirdly, the spatial circle fitting of contour points on each intersection line is carried out, and the radius characteristic curve is constructed. The fitting points are further screened by setting tolerance values. Finally, an improved particle swarm optimization algorithm is employed to perform spatial sphere fitting on the fitted points, achieving precise non-contact measurement of the spherical radius of the tooth surface. Experimental results show that the maximum absolute error of the proposed method is 0.029 mm, the maximum repeatability standard deviation is 0.015 mm, and the average measurement time of the algorithm is 4.56 s, which has high measurement accuracy and speed, and the whole measurement process is fully automated, which meets the requirements of enterprises for mass automated measurements.