The structrue of surface plasmon resonance sensors based angle measurement is complex and it is difficult to achieve on-line measurement. Based on surface plasmon resonance principle, a method of differential detection for refractive changes with light intensity is presented and two LEDs are used. Reference light path is designed to eliminate the light fluctuation. Theoretical analysis and experimental results show that the sensitivity of this method is twice as that of single-LED light intensity detection method. It is convenient to realize instrument miniaturization. Angle detection device and Spectrometer are not used in the system, and the system is potable and compact.