The research objective was to propose an analytic model to investigate the transient dynamic behavior of a tracked vehicle powertrain. Firstly, by considering the engine torque harmonics, gear backlash, friction coefficient and other nonlinear factors, lumped-mass component models as diesel engine, torque converter with lockup clutch, wet clutch, spur gear pair and vehicle were developed and then incorporated to an integral model. Then, a gear shift process that induces nonlinear dynamic behaviors, including clonk, gear contact loss and clutch stick-slip judder was simulated with the initial and boundary conditions for the shift process carefully set. Transient dynamic behaviors and the mechanism of dynamic behaviors occurred during the gear shift process were discussed. Finally, time-frequency analysis of output torque was conducted by wavelet transform. The instants of the occurrences of transient dynamic behavior were identified by time-frequency analysis and the corresponding frequency components were examined. The clutch torque pulse with a steep gradient due to the transition between slip and stick was an impact source in the system, and the results also indicated that the gear contact and reverse impact (114Hz) significantly impacted the output torque, the clutch stick-slip judder (1500~5000Hz) also affected the output torque but the high-frequency vibrations (higher than 5kHz) had little influence on it. The wavelet transform based time-frequency frequency analysis can be used to diagnose NVH issues of vehicle powertrain. Also, the system parameters of the powertrain can be optimized to obtain good NVH characteristics by using the simulation method proposed in the article.