In order to realize the parameter measurement of intelligent optical attenuator with different light energy, design a kind of rotary attenuation disk, and achieve field-bus motion control based on SIEMENS PLC. Introduced the design of rotary attenuation disk, and realized motion control according to SIEMENS S7-200 series PLC, constituted RS-485 field-bus with the free port communication. Research results show that the design can realize the accurate positioning control and remote control of rotary attenuation disk, at present, it has been put into normal operation and ensure normal optical experiment of a certain national large-scale facility.