Previous studies have proved that there is a highly localized object-based inhibition on nontargets in the Multiple Object Tracking (MOT) task. And researches have studied the mechanism of selective nontarget inhibition mainly through operating the characteristic contrast between non-targets and targets such as moving pattern, shape and stereo disparity, while the number of targets and nontargets stayed constant. Using Multiple Object Tracking with Probe Dot Detection task, the present study examined selective inhibition effects in Multiple Object Tracking when the number of targets or nontargets had changed.