The observed anomaly T is converted into the total gradient anomalywhich we call TT anomaly. The TT anomaly caused by a plate is characterizedby 1) being independent of magnetization direction; 2) having nothing to dowith dip angle of the georuagnetic field; 3) simplicity in shape of curve, i. e.nearly symmetrical; and 4) high lateral discriminability. Making inversion ofTT curve with the tangential method, we evaluated the top depth and magne-tization intensity of the plate. The relationship between the intercept of thetangential method and the top depth of the plate on TT curve is discussed indetail with the error range given.The computation speed of this method is rather high: it takes only 15seconds to invert a profile of 500 points on an AT personal computer.