Abstract: Circuit experiment is a very important professional basic course for students of electrical experiments. Experiment study is further validation of theoretical study and supplement. If the deviation between the experimental data and the theoretical value is large, it will not verify the theoretical value, instead it will make students feel puzzled. So if there is a problem, how to solve it? This paper is mainly from the experiment, numerical simulation and theoretical values to compare and determine the accuracy of measuring damping coefficient method under the condition of under-damped RLC second-order circuit. It also analyzes the reasons of the error, and then put forward the damping coefficient correction method.