AgBi₂I₇ thin film is one of the important candidates for constructing heterojunction ultraviolet photodetectors, due to their great optoelectronic properties and environmental stability. In this study, AgBi₂I₇ thin films were prepared by solution method and their photodetecting properties were investigated. By optimizing technological parameters such as concentration of the precursor solution and type of solvent (n-butylamine and DMSO), their photodetecting performance were investigated. AgBi₂I₇ thin films were fabricated on wide-bandgap GaN by optimal scheme to construct an AgBi₂I₇/GaN heterojunction. The heterojunction has a great selective detection of UVA-ray of which full width at half maximum is about 30 nm. Under 3 V bias and 350 nm UV irradiation, the On/Off ratio of the device exceeds 5 orders of magnitude, achieving a high responsivity of 27.51 A/W and a high detection rate of 1.53×10¹⁴ Jones. Therefore, the present research indicates that AgBi₂I₇ thin films prepared by solution method are promising to be applied to construct high-performance heterojunction ultraviolet photodetectors.