Abstract:  In order to measure the position of the gravity center of the bogie more accurately，the center-position test model based on the principle of torque balance principle is established，and the relationship between the center position of the bogie and the wheel of the bogie is analyzed． According to the principle of pendulum，the crane rocking method is established，and the relationship between the height of the bogie and the pendulum cycle is analyzed． After that，according to the principle of pendulum，the crane rocking method is established． Based on the test method of torque balance principle and the crane rocking method， the bogie center of gravity position is tested． The data obtained by the two test methods are analyzed and calculated to obtain the spatial coordinates of the bogie center of gravity position． The experimental cranerocking method results show that the relative error between the height value of the bogie and the theoretical value of the bogie test is 10. 47%，and the reproducibility of the test data is poor． On the other hand， the test result based on the torque balance principle shows that the coordinate of the bogie is basically the same as the theoretical value，and the relative error is less than 0. 5%，the test repeatability is good，which proved the accuracy and feasibility of the torque balance principle test model． 

Key words: rail way vehicles, bogie, center of gravity, torque balance, test methods, pendulum principle