In the field of microwave absorption, the quarter wavelength theory (QWM) is usually applied to film with multiple layers. However, it is demonstrated here that this is inappropriate since QWM is a flawed theory. The results for the conventional film with or without metal-back are usually applied to the middle layers in multilayer film. But this is inappropriate since there are incident microwaves at both sides of the middle layer but only the incident microwaves in front of the film are considered. No suitable theoretical treatment for multilayer film has been developed so far and this has been done in this work.