The invention relates to a thermal sealing package method and a thermal sealing package assembly of plastic films. Based on the conventional thermal sealing package method, a step of pressing two layers of the films tightly by using a positioning cut-off element before performing thermal sealing package on the thermal sealing package assembly is added, so that the films can be positioned reliably, which is favorable for thermal sealing package, and air flow between a packaging line and a packaging cavity can be cut off completely and the secondary pollution of harmful gas generated by the decomposition of the films during hot melting to packaging objects is avoided. An air pressure method or other mechanical cut-off method can be adopted in the thermal sealing package assembly. The thermal sealing package method and the thermal sealing package assembly are applied to the thermal sealing package of objects such as food, medicament, cosmetics and the like.