There are many kinds of harmonic generation or transmission electrical equipment in conventional DC transmission converter station. It is very important to establish a converter station broadband model for simulation study. However, the existing conventional DC converter broadband model and RTDS small step width broadband model of converter valve are not accurate enough. In this paper, according to the physical structure of conventional DC converter, converter valve and other components, the corresponding broadband equivalent model is established on RSCAD. According to the bandwidth impedance characteristics of related components, the appropriate impedance characteristic data fitting method is proposed to extract the converter bandwidth impedance model parameters. Finally, the simulation is carried out on RTDS hardware-in-the-loop simulation platform. The correctness of the modeling results is verified and the model accuracy meets the requirements.