In a traditional scanning imaging system, energy from target is usually weakened by the crossing-pixels phenomenon, and false alarms may happen because of random high intensity noise and peaks in a point target detection. To solve these problems the temporal-spatial over-sampling detection system was proposed. To evaluating its performance, the signal to noise ratio of image obtained by this system was compared with that obtained by single sampling in the same optical system. The results show that the signal to noise ratio can meet the requirement of applications by centralizing the target energy into a pixel in over-sampling system. The target scale can be larger than noise and peaks scale after high-resolution fusion and the target scale can be extended up to 3×3 pixels. Then the false alarm probability can be decreased effectively.