Corona discharges occur in high voltage electrical equipment in case of defects and damage, while ultraviolet(UV) light generated during discharge. High resolution imaging in the solar-blind UV bands has a lot of applications in corona discharge detection. A ultraviolet imager based on 320×256 solar-blind AlGaN focal plane arrays (FPA) was designed that work even in the sunlight, because the Cut-off wavelength of the AlGaN FPA is 280nm. The UV image signal processing system based on FPGA is composed of various function modules include the voltage bias, sequence drive, A/D data acquisition, non-uniformity correction, video transformation. Due to FPGA-based data acquisition and realtime image processing technology, the UV imager can operate at a rate up to 100 frame/s. The results show that the simulation high voltage ultraviolet image can be obtained by the UV imager. The image non-uniformity correction performed is one-points correction method to realize background subtraction. And the images show good uniformity and contrast. The UV image of the alcohol burner flame can be detected by the Ultraviolet Imager. Imaging quality was discussed which can be determined by signal-to-noise ratio (SNR), the integration time, the optics f/number and so on. The best imaging conditions were analyzed and the imaging system was designed and setup. The conclusion is proved that the ultraviolet imager based on solar-blind AlGaN FPA provides a new method for corona discharge detection of high voltage power transmission and distribution system.