A method for forming a protective film on an electronic module includes: placing the electronic module and a protective material placed on the electronic module in a chamber; performing a first heating procedure on the protective material in the chamber, and performing a first pressure boosting procedure, wherein a pressure in the first pressure boosting procedure is greater than 1 atmosphere; after softening the protective material, maintaining the first heating procedure, and performing an oscillating decompression procedure on the chamber, wherein the oscillating decompression procedure includes alternately changing pressures in the chamber between multiple low pressures less than 1 atmosphere; maintaining the first heating procedure, and performing a second pressure boosting procedure on the chamber, wherein a pressure in the second boosting procedure is less than that of the first boosting procedure and greater than 1 atmosphere; and performing a second heating procedure on the protective material in the chamber to form the protective film covering the electronic module.