A driver's airbag module assembly structure including: an inflator for generating gas by igniting an exploder; an airbag inflated toward a driver by the gas generated by the inflator; and a cage covering the inflator. A mounting plate is provided for accommodating the inflator, the airbag, and the cage in a cover member. A horn plate is installed between the mounting plate and a steering wheel. The mounting plate has a plurality of fixing clips formed at its outer surface. The cover member has a plurality of coupling holes coupled with the fixing clips and the horn plate is provided with a bracket having an angled tip and a fastening hole. The steering wheel is provided with a groove having an angled step corresponding to the bracket of the horn plate. Hooks of a mounting plate push flexible pieces formed at coupling holes of a cover to allow the mounting plate and the cover to be easily coupled with each other. In addition, since the hooks are closely inserted into lower horizontal holes, movement of the hooks can be reduced. Further, the hooks do not separate from the coupling holes when the airbag is deployed.