A novel sensing structure is proposed based on fiber Sagnac loop, and all fiber sensing for multi disturbance is realized. The sensing structure has the novel double Sagnac loop and WDM technology instead of traditional double light source, reducing the system error and realizing the measurement of multi disturbance. The analysis of sensing theory, deducing mathematical model and the simple and multi disturbance test are performed. The theory is proved experimently. Analysis indicates that the error is related to frequence response of demodulation circuit.