In this work, a high-power and broadband superluminescent diode (SLD) is achieved utilizing bimodal-sized quantum dots (QDs) as active materials. The device exhibits a 3 dB bandwidth of 178.8 nm with output power of 1.3 mW under continuous-wave (CW) conditions. Preliminary discussion attributes the spectra behavior of the device to carrier transfer between small dot ensemble and large dot ensemble. Our result provides a new possibility to further broadening the spectral bandwidth and improving the CW output power of QD-SLDs.