3D visual positioning is very important in position-based visual servoing for robot, directly affecting the control precision of the system. According to the robot with eye-to-hand and stereovision system, a direct method of visual positioning is proposed based on base coordinate system. It utilizes the corresponding relation of point to epipolar to establish homogeneous linear equations, for getting the fundamental matrix contained the relationship of relative position of two cameras. According to the properties of fundamental matrix, it is decomposed into projection matrix of two cameras relative to the base coordinate system of robot, so the method can reconstruct in the base coordinate system directly by equations of lines determined by planes in space. The method is simple and easy to be realized and the related experiment compared the measured coordinates with the actual coordinates, which shows that accuracy and efficiency of the method.