Abstract: In order to find a simple and reliable economical evaluation and test method of exhaust gas recirculation(EGR) rate so as to implement the closed-loop control of engine NO_x exhaustion, the difference of several different EGR evaluation methods is comparatively analyzed through engine jack horse experiment, and explore the probability of evaluating the EGR rates based on exhausted gas temperature and realizing NO_x closed-loop control, The experiment result show that in the given experiment condition， various evaluation methods will produce different EGR values, the maximum difference can be up to 8%，but the changing trends are the same.