An auxiliary supporting structure of a circuit board is for supporting at least one part of the circuit board. The circuit board has a CPU socket for connected to a CPU, and a through hole through which a heat sink fixing element passes. The auxiliary supporting structure includes a buffer body and a supporting element. In this case, the buffer body is disposed on a housing and has a first surface facing the circuit board. The buffer body is positioned between the circuit board and the housing. The supporting element is disposed on the buffer body and faces the through hole. The heat sink fixing element passes through the through hole and is fixed to the supporting element. An assembling method for the auxiliary supporting structure of the circuit board is provided.