Applications of the Long Range Surface Plasmon Resonance (LRSPR) technology from the SPRs are hard to be popularized because of its special film matching conditions, namely, the refractive index of the buffer layer must be similar to that of the tested sample. To improve the applicability of the traditional LRSPR technology, a symmetric LRSPR technology was proposed. A symmetric film structure ( buffer dielectric layer + metal film + buffer dielectric layer) was designed to break the limitations of the matching conditions and to further improve the penetration depth of electromagnetic field and the resonance peak depth. The symmetric film structure was analyzed theoretically, and an angular spectrum SPR detection system was built by using a Light Emitting Diode(LED) as the light source. The measuring system was used to measure the refractivity resolution of different glucose solutions, and the algorithm proposed was optimized. The results show that the refractivity resolution of the system can reach 6.1×10-7 RIU, the sensitivity is 1.22×105 pixel/RIU and a better linearity is obtained in a refractivity measuring range.