In the geotechnical engineering displacement monitoring, the choice of methods in monitoring depends on the condition monitoring. This paper used in the small Angle measurement method, angular intersection method, distance intersecting method, Total synthesis methods are studied. At present various documents, usually the coordinates calculation method are only gives. At best mean square error and mean square error of points in the direction of the coordinate. But mean square error in other direction is imponderable. Based on the above all sorts of monitoring method is deduced error ellipse, which can calculate the mean square error of monitoring points along each direction and estimate accuracy.