According to the geometric distortion of digital still camera, a detection method for geometric distortion based on digital image process is put forward. The cause of distortion for digital still camera and the principle of detection are expatiated. The target pictures captured by digital still camera are sent to computer and processed digitally by MatLab. The actual image′s figure is captured by pixel spacing, the ideal image′s figure is captured by geometric optics, and therefore the relative distortion is calculated. The experimental results show that this method can be useful for the digital examine and correction of digital still camera′s parameters for its simple process, easy realization and digital detection.