In order to guide the automatic decimal alignment of the parallel robot in the loading process, a high precision binocular measurement method of tanker mouth pose is proposed. The sub-pixels of the upper and lower edges of the tanker mouth image are extracted by image preprocessing. The binocular projection elliptical cone model of the spatial circle is established, and the bottom surface of the elliptical cone is constructed in the world coordinate system. Through the mapping relationship between the image pixels and the elliptic cone bottom, the optimal coordinate system of the cone bottom is found to obtain the target pose. The position of the pixel corresponding to the real center is calculated by pose correction, and the three-dimensional coordinates of the center in the world coordinate system are obtained by binocular triangulation. Aiming at the ambiguity problem of spatial circle projection, an ambiguity elimination method based on the tanker mouth height is proposed. The results of the simulation and experiment show that the algorithm has high accuracy and can meet the requirements of large angle pose measurement. The maximum error of the measured pose is 1. 8°, and the maximum error of the real center pixel extraction is 0. 98 pixels. The method does not need any auxiliary measurement and constraint conditions, and effectively improves the automatic efficiency in the loading process.