As reference-frame-independent quantum key distribution (RFI-QKD) protocol can make quantum key distribution (QKD) system obtain the ideal key rate and transmission distance without reference system calibration, thus it has attracted much attention recently. A new RFI-QKD protocol based on wavelength division multiplexing (WDM) is proposed. In this protocal, Alice prepares multiple signals of different wavelengths and transmits them to the receiver Bob by using WDM technology. After receiving the optical pulse, Bob uses the wave decomposition multiplexer to separate the signals of different wavelengths and then measures them, and at last calculates the final security key rate by combining the decoy state. Simulation results show that the key generation rate based on WDM RFI-QKD is affected by multiplexing channel number and transmission distance, and it increases with the increase of multiplexing channel number. Therefore, introducing of WDM technology is an effective way to improve key rate.