This paper investigates the behaviour of the reverse-bias leakage current of the Sehottky diode with a thin Al inserting layer inserted between Al0.245Ga0.755N/GaN heterostructure and Ni/Au Schottky contact in the temperature range of 25-350℃.It compares with the Schottky diode without Aluminium inserting layer.The experimental results show that in the Schottky diode with Al layer the minimum point of I-V curve drifts to the minus voltage,and with the increase of temperature increasing,the minimum point of I-V curve retus the 0 point.The temperature dependence of gate-leakage currents in the novelty diode and the traditional diode are studied.The results show that the Al inserting layer introduces interface states between metal and Al0.245Ga0.755N.Aluminium reacted with oxygen formed Al2O3 insulator layer which suppresses the trap tunnelling current and the trend of thermionic field emission current.The reliability of the diode at the high temperature is improved by inserting a thin Al layer.