An apparatus and method for automatic power adjustment of an optical network system are provided by the present invention. In the automatic power adjustment system which includes a plurality of electric-adjustable optical attenuators and a power adjustment module configured in a network management board: each OA board, i.e. optical amplification board and each service forwarding board respectively report their power relevant parameters to the power adjustment module; the power adjustment module judges whether an adjustment is required for an OA board and/or a service forwarding board after performing calculation according to the power parameters reported by each OA board and each service forwarding board, and when determining that the adjustment is required, triggers the adjustable optical attenuator on the corresponding OA board and/or the service forwarding board to perform the power adjustment.