The work process of the plastic extrusion machine and the characteristic of the tension control in the product line of BOPP were introduced. Aiming at the current problem of tension control in extrusion machine, a project was proposed that applied the frequency control technique to the tension control of extrusion machine. The practical test shows that the project of applying VG7 inverter in the extrusion machine can realize the constant tension control, improve the adjustable frequency precision, decrease the cost and operate conveniently, run steadily, and has great market value.