According to the valve pulse loss phenomenon during debugging stage of Gaoling back-to-back HVDC system, the influence of valve pulse loss on the HVDC system operation and the protection coordination were investigated. The fault type of pulse loss has been dissertated, and the simulation results of PSCAD/EMTDC were demonstrated to verify the validity of the fault analysis. The research results provide theoretical guidance and help for the operation and maintenance of HVDC converter station on site.