1. A computer-based method for fitting feature elements using a point-cloud of an object, the method being executed by one or more processors of the computer, and the method comprising: receiving the point-cloud of the object from a point-cloud obtaining device by one of the processors; constructing a triangular mesh surface of the point-cloud by one of the processors; determining a plurality of uppermost boundary points of the triangular mesh surface by one of the processors; fitting a feature element according to the uppermost boundary points by one of the processors, comprising: receiving a fitting type of the feature element; fitting the uppermost boundary points to form a fitted plane upon condition that the fitting type is a line type or a circle type, and projecting the uppermost boundary points on the fitted plane to produce projected points; obtaining a corresponding iterative equation according to the fitting type; receiving an iteration frequency N and a number of points used in each iteration; computing original iterative parameters using the uppermost boundary points or the projected points with a least square method; computing an iterative value of the uppermost boundary points or the projected points according to the original iterative parameters and the corresponding iterative equation; computing feature values of the feature element to be fitted according to the iterative value; and fitting the feature element according to the feature values and the fitting type; and creating the feature element by one of the processors and outputting the feature element to a display.