The invention discloses a moving target detecting method based on background reconstruction, comprising the following steps: inputting an image sequence and computing the gray level difference of the adjacent frames of the pixels; classifying the stable gray level intervals; computing the mean gray level of each class of stable gray level intervals; merging the similar classes of stable gray level intervals; selecting the background gray levels of the pixels; and detecting the moving target. The method saves storage space, is small in computed amount, good in robustness and wide in application range, dispenses with establishing models of the backgrounds and targets in the scenes and can directly reconstruct the backgrounds from the scene images containing moving foreground and effectivelyavoid mixing. The method has extensive application prospect in such real-time system fields as machine vision, video monitoring, military science, urban traffic monitoring, daily resident safety monitoring, etc.