The invention discloses a method for automatically detecting a touch object by a camera, which comprises the following steps of: firstly accumulating capture image line gray values and finding out theminimum or the maximum of accumulated sums; then determining image acquisition areas; and finally making comparison of the accumulated sums of gray values of each column of images taken respectivelywhen the touch object exists and when no touch object exists so as to realize the auto detection on the touch object. The method has the advantages of little operand, quick response speed and the likecompared with the prior art.