The present invention discloses a method for transmitting data and a gigabit-capable passive optical network system, which method comprises: a transmitter carrying indication information in an uplink or a downlink frame transmitted to a receiver for enabling the receiver to discard information which does not need to be processed by the receiver in the uplink or downlink frame according to the indication information. The data type transmitted by GPON systems is expanded and the idle bandwidth is effectively handled by the present invention.