Military unmanned ground vehicles are often used in wild natural environment, autonomous following and accompanying security are typical functions. In order to make a quantitative assessment about the autonomous following performance of unmanned ground vehicles on unstructured scenarios, a set of evaluation index system construction method is proposed based on the combination of risk analysis and key performance indexes. First, the kinematics model of autonomous vehicle following in straight and curve based on meta-trajectory is established. Second, the key indexes affecting the following performance are analyzed and obtained from collision risk and lost risk. Third, the evaluation index system of autonomous following performance is constructed from five dimensions: average following speed, collision risk, collision hazard degree, following stability and lost risk. Finally, two unmanned vehicles are tested, the results show that the conclusion based on the constructed evaluation index system can significantly reflect the difference of autonomous following performance, which is basically consistent with the subjective evaluation of the test personnel.