A system for deploying a side airbag of a vehicle comprises a front/side airbag controller for controlling processes of deploying a front airbag and a side airbag independently. The front/side airbag controller comprises a front signal monitoring unit converting a front acceleration signal received from the airbag controller into a speed according to time and then determining whether or not the speed according to time exceeds a first threshold. A threshold adjustment unit receives a threshold adjustment request signal from the front signal monitoring unit to lower a second threshold that is a threshold with respect to decision factors for deploying the side airbag.