The central transmission gear system of turboshaft engine is the core component of helicopter power transmission. Notwithstanding, under the influence of onerous loading and fluctuating cyclic stress, the root region of a bevel gear is susceptible to the initiation of fissures, which may ultimately culminate in catastrophic tooth fracture. Once a fault occurs, it will seriously endanger flight safety. Consequently, this dissertation is dedicated to the investigation of dynamic characteristics pertaining to crack defects in the central drive bevel gear of a turboshaft engine. By establishing a dynamic model with cracks, the vibration response under complex working conditions is analyzed. The effect of crack propagation on the natural frequency, stress distribution and vibration amplitude of gear is discussed by means of modal analysis and harmonic response analysis. The results show that the stress value of the cracked gear is significantly higher than that of the normal gear under the specific high frequency excitation, Moreover, the presence of such cracks can alter the stiffness and damping properties of the gear system, thereby suppressing the vibration amplitude. These findings provide an important theoretical foundation for early-stage fault diagnostics and online health monitoring of the turboshaft engine central transmission gear system, and help to improve the reliability and flight safety of the engine.