During the movement of the monocular robot, the camera pose cannot be recovered due to the extremely short base line between the key frames.Aiming at this problem, an iterative optimization algorithm of essential matrix was proposed to quickly decompose the relative pose relationship of robot by using the known specific reference objects. In this method,firstly, the estimated value of essential matrix is obtained using a specific reference with clear three-dimensional information. Then, the essential matrix is iteratively optimized with the matched feature point groups of adjacent key frames and the estimated value of essential matrix. Finally, the estimation of translation vector is obtained by the constraint relation of essential matrix, and the estimation of rotation matrix is obtained based on Lie group. The unique solution is obtained by further optimization. The problem that the relative pose of the camera cannot be restored due to the too short base line is avoided in this method. The experimental results show that the relative pose relationship of the robot can be quickly solved and optimized in this new method, and the absolute error of relative displacement estimation is less than 0.03 m, which is superior to the traditional method.