Abstract: The short channel effect of high-frequency gallium nitride microwave power devices is an important reason that limits their radio frequency performance. The back-barrier structure is usually used to improve the confinement of the two-dimensional electron gas and suppress the short channel effect. However, the addition of a back-barrier layer will increase Parasitic resistance and gate capacitance which reduce the cut-off frequency f_t and maximum oscillation frequency f_max. Therefore, a graded aluminum component aluminum gallium nitride back-barrier structure is adopted, which improves the f_t and f_max to a certain extent. The results show that compared with the fixed component back-barrier, the f_maxof the gradient component back-barrier device has increased by 11.1 GHz to 150.9 GHz. Its radio freuqncy power characteristics have also been significantly improved. When the operating frequency is 8 GHz, the maximum power density reaches 5.2 W/mm, the power gain reaches 14.8 dB and the power added efficiency reaches 30.3%.