Screw is a common component of material conveying. Inventor can't be used to draw complicated curve directly by the equation of curve. So variable pitch screw can't be draw directly by using Inventor. For this reason, the use of Inventor in packaging machinery design is limited. A new way of drawing variable pitch screw was put forward by using the 3D modeling function of Inventor combined with function calculation of Matlab. The result showed that through this way, variable pitch screws can be draw easily and accurately. Besides, the weakness of Inventor in drawing complicated component is compensated, and Inventor can be used more widely in machinery design.