Abstract: High quantum efficiency, high UV/VIS rejection ratio, fast response and wide spectral response are the main objects for the design of AlGaN photodetectors. To obtain suitable detector structure for UV focal plane array, combining with the characteristics of epitaxial materials grown by MOCVD, a design of back-illuminated solar-blind AlGaN photodetectors with high quantum efficiency was demonstrated based on simulations and experiments. The design basis and process of the AlxGa1-xN-pin photodetectors were introduced in detail, and then the design was optimized by experiments. Moreover, the photodiodes were fabricated according to the design, and the performance of device was also presented, exhibiting high peak unbiased EQE of 57% at 270 nm, responding to the spectral range between 250 nm and 282 nm. It is indicated that an optimal design is achieved.