The method which employs the frame accumulation and shaped function is effective in low-light-level imaging. However, it has drawbacks of lower imaging speed and complex operation. To optimize the method, we provide the design of an improved low-light-level imaging system with higher detection sensibility. The design is developed specifically for a faster imaging speed based on field programmable gate arrays. It features the use of least-square algorithm and a saw-tooth wave varied light applied to the image sensor. By manipulation of the video signal in synchronous dynamic random access memory, a low-light-level image which was previously undetectable can be estimated. The design simplifies the imaging process and doubles the imaging speed, and makes the system adapted to long range imaging.