Abstract: The common pulse transmission modes in rotary steering drilling including drilling fluid pulse transmission,cable transmission,acoustic wave transmission and electromagnetic wave transmission were analyzed.The drilling fluid negative pulse transmission mode was selected to send the instruction signal to the modulating rotary steering tool.The overall scheme of the drilling fluid negative pulse signal transmission was designed.According to the change of pump displacement,three-descending and three-ascending pulse transmission modes were proposed by comprehensively considering short instruction transmission and the accurate identification.Considering the need of instruction transmission,the limit condition of magnitude and orientation of the guiding force,and the downhole storage capacity,three-descending and three-ascending ternary-notation negative pulse encoding combination mode was optimized.The receiving of downhole signal was achieved by detecting the current or frequency change of the downhole generator.The laboratory experiment proved that the method was reliable.The integrative command control software system was developed.