The invention discloses a new method for automatically measuring the height of a foreground object by using a picture which is returned by a single camera. In the method, digital image processing technology is adopted; and the method comprises the following steps of: acquiring mapping relation of pixel points between an image plane and a world coordinate system by scaling during calculation of the foreground height, namely calculating a homographic matrix HgMatrix, a vanishing point mv in the vertical direction, a vanishing point mx in the transverse direction and a vanishing point my in the longitudinal direction so as to calculate a projection matrix ProMatrix between the world coordinate system and an image plane coordinate system; acquiring a high point highnod and a low point lownod of a foreground area and calculating a true high point truehigh and a projection point, namely true low point truelow, of the high point highnod on a ground plane; and finally calculating a distance value between Z value of the true high point truehigh and a time coordinate point corresponding to the lownod and the truelow and acquiring a more accurate estimated value of the height of the foreground object according to Pythagorean proposition. The method solves the problem of height measurement of an oblique foreground object and improves the accuracy of height estimation and measurement of the foreground object; and because the measurement method of the single camera is adopted in the method, the cost of actual application is reduced.