Proposed are a seat side bolster apparatus and a control method thereof. The seat side bolster apparatus of the disclosure includes a driving unit, which is provided under a foam pad of a seat cushion, is moved upwards and downwards by operation of an actuator, and presses the foam pad upwards when moving upwards, and a covering bracket, which is connected to the driving unit so as to be moved upwards and downwards together with the driving unit and to which an end of a covering enveloping the foam pad of the seat cushion is fixed.