Based on the current application requirements for wideband response photodetectors， we designed a novel silicon avalanche photodetector （Si APD） with high response in a broad spectral range of 250 -1 100 nm and it could achieve efficient detection of ultraviolet， visible and near-infrared light without splicing. The enhancement of silicon on ultraviolet and infrared bands was separately analyzed. This was followed by simulation on the device structure designs using different methods such as back incidence， to improve short wavelength absorption while maintaining a high infrared absorption. The Si APD shows a peak wavelength at around 940 nm and a high photoresponse at 250 nm and 1 100 nm which exceeds 15% of the peak responsivity. This type of device is suitable for multispectral applications and future high-precision detection.