Binding sialates to hemagglutinin-neuraminidase (HN) activates (triggers) the fusion protein (F) to start the membrane fusion process of paramyxovirus, but the mechanism by which the HN and F associate with each other to induce membrane fusion is still unclear. It is noteworthy to study the interaction domains of HN and F of paramyxovirus. To screen interacting domains of the HN and F proteins of Avian parainfluenza virus-2 (APIV-2) and identify the structure of binding proteins, the GST pull-down assay and mass spectroscopy (MS) and circular dichroism (CD) experiments were performed in this study. The study revealed that the globular head region of HN protein tends to form a complex with either the heptad repeat 1 (HR1) or the heptad repeat 2 (HR2) of F protein respectively. This paper discusses the novel fusion mechanism induced by paramyxovirus HN and F proteins.