Abstract: In this paper the principle,calculation procedure and computer programming of Method of Discrimination of Tangential Direction are described.This method controls the movement of the plotter head based on the characteristic that the curve can divide the plane into positive and negative areas.The plotter head thus goes forwards according to tangent slope of the curve.This method plots successfully a general plant curve f(x,y)=0 using eight vectors and thus accuracy and velocity of the computer assisted map drawing could be increased.