To overcome the difficulty on objective measurement of shift comfort of automatic mechanical transmission(AMT) , the feasibility and advantages of using second derivative of the transmission input shaft speed was confirmed to calculate the gear-shifting jerk. The calculation process of jerk was elaborated in more details and jerk nondimensionalization was performed for control necessity. Finally, the indirect measurement sampling period was determined by test methods. Vehicle tests show that the indirect measurement technology can be used for control feedback and objective evaluation of AMT.