Fabry-Perot cavity (F-P) sensor has simple structure and strong multiplexing ability.It has high sensitivity to the physical quantities that lead to the changing of cavity length;it has been paid more and more attention in the field of ultra precision measurement.In order to measure two targets with a set of fiber F-P cavity,an F-P cavity interference system with mixed two feedback signals in the cavity is designed.At the same time,conducted on micro vibration measurement of two channel sand obtained the mixed interference signals of two feedbacks F-P.It has the high and low frequency signal spectrum by many times of envelope decomposition and then calculated amplitude of the target to be measured.The results show that the amplitude error of the target to be measured is 6.63 % by high frequency signal and 1.32 % by low frequency signal.The amplitude measurement of two micro vibration signals is realized effectively,the measurement channel of F-P cavity is expanded,and the anti-interference ability is improved.The results show that the amplitude error of the target to be measured is 1.32 % by low frequency signal and 6.63 % by high frequency signal.It could effectively realize the measurement of two micro vibration signals,expanded the measurement channel of F-P cavity and improved the anti-interference ability.