1. A method for generating an n.times.n subpixel mask of a pixel for antialiasing by receiving .DELTA.X and .DELTA.Y values of an edge having a slope and an initial value of a cross distance, the method comprising the steps of: forming subblocks by dividing the pixel into n subblocks depending on the slope; calculating a subblock coverage by: determining a pair of reference points depending on the slope of the edge, calculating cross distances (de) defined by the distance from one of the reference points to an intersection point of the edge and a pixel boundary, subtracting a slope ratio value from a first cross distance after calculating a corresponding cross distance from the initial value of the first cross distance by an interpolation method and calculating slope ratio values of the formed subblocks, including calculating a slope ratio value (m.sub.k), by drawing a first line parallel to another pixel boundary line at the intersection point and then obtaining a distance from the first line to the edge, in the subblock units, and calculating the subblock coverage (h.sub.k) as h.sub.k =de-m.sub.k ; and generating an n.times.n subpixel mask depending on the calculated subblock coverage, whereby aliasing generated at the edge is removed.