Traditional surface plasmon resonance sensors have the shortcoming of needing expensive rotation or the spectrum equipment, so the method of differential detection for refractive changes with light intensity is presented and two LDs are used. This method is based on the surface plasmon resonance principle and variation of the refractive indices is measured by the optical intensity of two different wavelengths. The reference light path is designed to eliminate the fluctuation of light. Theoretical analysis and experimental results show that the sensitivity value of this method is twice as much as that of single-LD light intensity detection method, easy to implement instrument miniaturization. The angle detection device and the spectrometer are not used in the system, so the system can be potable and compact. Adjusting the incident angles and different wavelengths of light can be used to detect different range of refractive index.