With two level demodulation,the demodulate rule of WDM/SDM FBG sensing system was optimized. To improve the demodulated speed of sensing system more,a FBG sensing multiplexing technique with Rmuti-demodulate device was proposed. Petri net theory was used to sovle the harmonize problem of the technology. In order to demonstrate the feasibility of the multi-demodulate technique,a FBG sensing system with four sensing channels and two F-P filters were studied. The performance of the technique was analyzed by using Queuing Theory. The average delay time of the double demodulate system is lower one magnitude order than the conventional ones.