The present application provides a package sealing structure, a preparation method thereof and a flexible packaging battery. In a package peripheral region of the package sealing structure, the insulating heat sealing layers of the two layers of packaging film face each other and are melted into one body to form an insulating fusion layer which seals and bonds the two layers of the packaging film together. The insulating fusion layer is formed with an overflow portion that overflows from the package peripheral region of the package sealing structure to the outer end surfaces of the core metal layers of the two layers of packaging film and covers completely the outer end surfaces of the core metal layer of the two layers of packaging film, so that the outer end surfaces of the core metal layers are insulated from the peripheral environment.