The invention relates to a novel road side boundary design method. According to the road side boundary design method, a road side boundary is represented by a plane normal curve, and meanwhile a novel offset-distance changing function is provided. When the plane normal curve is used for representing the side boundary, line types of a central line do not need considering, a calculation model is simple, and designing is convenient. The offset-distance changing function is obviously characterized in that side boundary has a variable starting point and an end point without turning points, the curvature change changes from big to small and then to big, the change meets the running track of an automobile, the side boundary is smooth in line type, and the area of a road can be reduced. The road side boundary design method overcomes the defects of traditional linear distance changing and high-level parabola distance changing that the curvatures of the variable starting point and the end point are discontinuous, turning points exist, and the running track of the automobile is not met; when the central line is a curve, the width of the side boundary of the end with a large offset distance is large, and the width of the side boundary of the end with a small offset distance is not enough. The method can be applied to design of medial strips and side strips of roads.