Abstract: By an optimized fabricating process, a kind of solar-blind ultraviolet photodetector was designed and fabricated used AlGaN material grown on sapphire substrate by metal organic chemical vapor deposition(MOCVD) method. The external quantum efficiency gets well improved. The structure of the device is back-illuminated p-i-n type. Al mole factor is 40% in both p and i type layers and it is 65% in the n type lawyer. The shape of the device is a circle and its diameter is 500 m. The spectral response of the device starts form 260-310 nm while its peak response occurs at 283 nm. Under zero bias, a dark current density of 2.710-10 Acm-2 and a responsivity of 13 mA/W are found which corresponds to a parameter R0A of 3.8108 cm2 and a detection rate of 1.971012 cmHz1/2W-1. Under -7 V bias, the responsivity reaches to 148 mA/W, corresponding to an external quantum efficiency of 63%.