The parameters of a stereo camera directly determine the accuracy of a stereo vision positioning system. In this paper, the relationship between camera parameter error and positioning error is established by using the geometric analysis method with a clear physical meaning. The error models of the relative position error and camera resolution error of the stereo camera are established. The relative position error of the stereo camera is represented by the rotation and translation of the coordinate system, and the positioning error is derived from image coordinates through the pinhole camera model. For the camera resolution error, the two pixels of the stereo camera are projected into an octahedral uncertain region in space. We use geometric methods to derive the maximum size of the octahedron in the three-axis direction. The maximum size in the three-axis direction is used to evaluate the impact of camera resolution errors. The depth of field and angle of view are used to represent the measured area. The effects of resolution error and camera parameters on the measurement error of each axis are analyzed. Finally, a large number of simulations verified our conclusion. By comparing the effects of the magnitude of the error, we can conclude that the baseline and pixel size of the camera have a greater impact on the positioning accuracy.