Abstract: Aiming at the two-way communication function between the host computer and multiple unlocking disks of the interval integrated monitoring system, in order to simplify the system structure as much as possible, this paper determined communication mode and formulated the special communication protocol through the analysis and research of RS-485 bus technology and ProfiBusDP protocol.The paper presented a communication scheme of RSSP-I secure communication protocol based on RS-485 bus technology and call response mechanism, which implemented stable communication between host computer and unlock disk without adding hardware communication equipment. The proposed communication scheme can meet the communication requirements between the host computer and the unlocked disk, and simplify the system structure.