1. A method for extraction of subpixel accuracy edge in photogrammetry, comprising the steps of: a. capturing into a computer a picture, of which edges is to be extracted; b. defining four neighboring pixels which form a square as one cell; c. recognizing the type of each cell composed of the four pixels; d. finding out side or sides of a cell that intersects with a part edge, and determining the subpixel accuracy coordinates of the intersection points by linear interpolation; and e. connecting the intersection points, to extract the part edge.