This study begins with the fabrication and simulation of high-performance back-illuminated AlGaN-based solar-blind ultraviolet (UV) photodetectors. Based on the photodetectors, a low-noise, high-gain UV detection system circuit is designed and fabricated, enabling the detection, acquisition, and calibration of weak solar-blind UV signals. Experimental results demonstrate that under zero bias conditions, with a UV light power density of 3.45 μW/cm² at 260 nm, the sample achieves a peak responsivity (R) of 0.085 A∙W^-1, an external quantum efficiency (EQE) of 40.7%, and a detectivity (D*) of 7.46×10¹² cm·Hz^1/2·W^-1. The system exhibits a bandpass characteristic within the 240—280 nm wavelength range, coupled with a high signal-to-noise ratio (SNR) of 39.74 dB.