A motion detection method is applied to a monitoring camera apparatus with motion detection function. The motion detection method includes analyzing a pixel value of each frame from a video stream changed over time, defining a first period and a second period having the pixel value greater than a triggering threshold respectively as a first event and a second event, comparing a time length of the first period with a filtering threshold to acquire time difference between an end point of the first period and a beginning point of the second period, comparing the time difference with a merging threshold, and acquiring relation between the first event and the second event according to comparison results of the filtering threshold and the merging threshold, so as to determine a detecting period of the motion detection function for actuation.