Abstract: In order to study the vibration characteristic of composite honeycomb structure under hygrothermal condition, the natural frequencies of honeycomb structure composed by carbon fiber/bismaleimide composite laminate and Nomex core were numerically analyzed under different temperatures and humidities. Based on the piecewise shear deformation theory, considering the honeycomb thin plate and thick plate respectively, the eigenvibration equation of composite honeycomb structure was solved by finite element method using the equivalence of temperature and humidity. A detailed model of composite honeycomb structure with four-edge clamped support was established by using finite element software ABAQUS. The effects of temperature, humidity, and combined temperature and humidity on the vibration characteristic of composite honeycomb thin plate and thick plate were discussed respectively. The numerical results show that compared with the increase of temperature, the natural frequencies of honeycomb structure are more sensitive to the increase of moisture concentration. Under the same humid and thermal environment, the natural frequency of the thick plate structure is larger than that of the thin plate, and the higher order of natural frequency, the greater the increase of natural frequency. The coupling effect of temperature and humidity has a greater effect on the natural frequency of composite honeycomb structure than the superposition of temperature and humidity when they act alone, and this effect is more obvious for the composite honeycomb thin plate.