According to the practical courses of drawing mapping for the students majored in mechanics in higher vocational colleges and universities, this paper analyzes the problems neglected by the students in drawing mapping teaching such as the measurement precision, inaccurate expression for spare parts, tiredness of finishing drawing and so on, proposes to introduce 3D modeling into drawing mapping teaching, to raise the precision for the expression of spare parts by taking the advantage of the conversion between 3D model and 2D drawing, to use 3D assembly to constrain the precision of spare parts size measurement, and to generate 2D engineering drawing directly from 3D model, which greatly boosts the speed and accuracy of the drawing and which befits modern design idea.