A method for checking a boundary line graph using a computing device. The computing device adds a segment line between two adjacent endpoints of the boundary line graph, if the two adjacent endpoints are not connected using the segment line. The computing device removes the segment lines of the endpoints corresponding to intersection points, if the number of the intersection points is not equal to the number of the endpoints. The computing device changes label characters of the endpoints to be arranged in a predetermined order, if an order of the label characters of the endpoints is not a predetermined order according to the boundary line vector.