1. A line guided three-dimensional model reshaping method applied on a computer system, comprising: step S 100 , creating, by a processor of the computer system, a two-dimensional (2D) line database: extracting a 2D contour of an object from an Internet image containing a single object by using an image segmentation algorithm, and creating a 2D line database by selecting a 2D contour or a 2D main skeleton based on symmetry of the object; step S 200 , retrieving and suggesting, by the processor of the computer system, a 2D line: selecting, by a user, an editable region in an input three-dimensional (3D) model; extracting a 3D editable line; and suggesting a corresponding 2D contour or skeleton in the 2D line database based on a shape context descriptor and a shape feature; step S 300 , contour matching and parametric deformation performed by the processor of the computer system: establishing a point-to-point correspondence between the 2D contour or skeleton and the 3D editable line; and reshaping the 3D model by using a parametric deformation algorithm; the retrieving and suggesting, by the processor of the computer system, a 2D line in step S 200 comprises: step S 210 : extracting an editable line from an editable region selected by a user in an input 3D model, wherein the editable line of the 3D model comprises: an axis, a cross-section and an outline; calculating a shape context distance SC(l i , l j ) between the 2D contour or skeleton l i , and the 3D editable line l j , and a length-to-width ratio diversity distance ∥p(l i )−p(l j )∥ 2 2 of a normalized oriented bounding box (OBB) of each line; and evaluating a distance metric between the 2D contour or skeleton and the 3D editable line by calculating a weighted sum of the shape context distance and the diversity distance: 
 D ( l i ,l j )=(1−ω) SC ( l i ,l j )+ω∥ p ( l j)− p ( l j )∥ 2 2 ; and step S 220 : selecting and suggesting a 2D contour or skeleton having the shortest distance metric D(l i ,l j ) to the 3D editable line by adjusting the weight ωof the previous step, wherein the axis of the 3D model is matched to the 2D main skeleton in the 2D line database and the part of 2D contour on one side of the symmetrical axis, and the cross-section and the outline are matched to the reflectionally or rotationally symmetrical 2D contour in the 2D line database.