The best thickness of release agent was researched in order to get ideal adhesion of transfer printing ink in the process of transfer printing. The surface of PET film was coated with release agent of different thickness and different mass ratio under 25 ℃, different pressures, and different spread speeds. The surface of release agent was coated with transfer printing ink after drying. Peeling experiments were carried out on the coated films. The results showed that ideal peeling effect can be achieved when coating speed 0.1 m/s, pressure 300 N, thickness 9 μm, and mass ratio 3∶1.