How to detect a moving object fast and correctly in a complicated surrounding is one of the most important issues to be solved. Insects could catch a shift in their view field and make an action to prey or flee, which indicates they have peculiar capability to acclimatization. Fly visual system was modeled with an Elementary Motion Detector (EMD). We chosen first-order IIR digital filter as the time delay unit and made the Difference of Gaussians method to extract more details and eliminate random noise. We carried out simulation experiment based on software Matlab to detect a moving auto. From the result, this method can detect the moving object without the distraction by complicated environment.