Abstract: The wellbore pressure fluctuation caused by negative pulse downlink communication in rotary steerable drilling is unfavorable to well control safety. Therefore, based on the operating principle and characteristics of the negative pulse downlink communication system, a managed pressure balance method with standpipe pressure as the reference and a wellbore transient flow model were established. The flow law of drilling fluid in the wellbore during negative pulse downlink communication was analyzed, and the effect of the managed pressure balance method based on standpipe pressure was verified. The numerical simulation results show that the signal propagates from the standpipe to the wellhead during the negative pulse downlink communication, and the flow rate fluctuation is significantly distorted; the pressure fluctuation is significantly reduced, both of which have time delay effects. The variation pattern of standpipe pressure and bottom hole pressure is basically consistent, proving that standpipe pressure can be used as reference data for regulating back pressure. The negative fluctuation of bottom hole pressure is decreased by 80.9% during downlink communication under managed pressure, and the fluctuation pattern of the bottom hole flow rate is basically consistent with that under constant wellhead back pressure. The research results indicate that this managed pressure balance method with standpipe pressure as the reference can effectively suppress the fluctuation of bottom hole pressure during negative pulse downlink communication and maintain stable bottom hole pressure, and it does not interfere with the flow signal of the negative pulse downlink communication, providing theoretical guidance for on-site operations.