A motion detection method is adapted for an image display circuit including a motion detection circuit and an arbitration circuit. In this motion detection method, a number of motion quality observation windows are defined. Each motion quality observation window includes a start point and an ending point. In the motion quality observation windows, a write frame count value is adjusted according to a write frame command. At the end point of each motion quality observation window, if the write frame count value is equal to or bigger than a preset count value, an enable signal is outputted to the arbitration circuit to determine whether the image display circuit performs motion display. In the motion quality observation windows, the end point of the i-th motion quality observation window is located between the start point and the end point of the (i+1)-th motion quality observation window, where i is a positive integer.