A system that automatically adjusts a threshold value of cross color suppression and a method thereof are disclosed. The system includes a cross color suppression unit, a statistical unit and an adjustment unit. The cross color suppression unit is for receiving input video data and searching a plurality of cross color dots thereof. According to a threshold value, the cross color suppression unit determines whether the cross color dot is static or dynamic, suppresses the static cross color dot and then generates an output video data. The method used by the present invention is, the statistical unit calculates residual cross color amount of the output video data that has been suppressed. Then, the adjustment unit compares the cross color amount of the output video data with a reference value so as to send a corresponding adjustment signal to the cross color suppression unit to adjust the threshold value.