The principle of three-dimensional(3D) laser scanning technology for deformation monitoring is to analyze the point cloud data measured at different time intervals and determine the deformation area and the deformation amount in the monitoring object based on the contrast of the obtained data. Compared with the traditional single-point measurement technology, the 3D laser scanning technology has advantages such as high efficiency, high precision and large amount of measurement data. However, no evaluation is made on the reliability of monitoring results when applying this technology for deformation monitoring. Therefore, it is necessary to analyze the point cloud error and determine the indicators of point cloud deformation monitoring. In determining the point cloud error space, we introduce the error entropy to eliminate the influence of the error between adjacent points and control the influence of the uncertainty of the error space. According to the relationship between the error entropy and the extreme value of the error, the indicators of point cloud deformation monitoring can be finally determined. The feasibility of the indicators are verified based on the flat panel simulation experiment, and then applied to the bridge deformation monitoring.