The disclosure discloses a method and device for measuring received optical power of an Optical Network Unit (ONU), which comprises: acquiring a bandwidth and/or byte width required for measuring a Received Signal Strength Indicator (RSSI) according to a type of an optical module at an Optical Line Terminal (OLT) side, and notifying the bandwidth and/or byte width to a Dynamical Bandwidth Assigned (DBA) module at the OLT side; distributing, by the DBA module, the bandwidth and/or byte width to the ONU which needs to measure the RSSI; and sending, by the ONU, an uplink optical signal to the optical module according to the bandwidth and/or byte width; and measuring, by the optical module, the RSSI value according to the received uplink optical signal. By using the method and device provided by the disclosure, the received optical power of the ONU at the OLT side can be measured accurately, and the requirements of a Service Level Agreement (SLA) and the RSSI can be met simultaneously when the DBA module distribu
