A motion object detection method using an adaptive background model and a computer-readable storage medium are provided. In the motion object detection method, a background model establishing step is firstly performed to establish a background model to provide a plurality of background brightness reference values. Then, a foreground object detecting step is performed to use the background model to detect foreground objects. In the background model establishing step, a plurality of brightness weight values are firstly provided in accordance with the brightness of background pixels, wherein each of the brightness weight values is determined in accordance with the relative background pixel. Thereafter, the background brightness reference values are calculated based on the brightness of the background pixels and the brightness weight values. In addition, a computer can perform the motion object detection method after reading the computer-readable storage medium.