A novel single-ended reflecting Long Period Fiber Grating (LPFG) sensor with thin metal film overlay and the sensing system is described. An all-fiber reflection LPFG sensor with three-layer structure (core, cladding and metal) based on Surface Plasma Resonance (SPR) is established experimentally and fabricated with a pulsed CO₂ laser writing system and vacuum evaporation coating system. Different nm-thick thin metal films are deposited on the reflected LPFG sensor for the excitation of Surface Plasma Waves (SPWs) and the characteristics of the reflection resonance spectra of the LPFG sensor for measuring refractive index of fluids are studied. In atmosphere condition, the peak wavelength shifts about 1.14 nm as the sensor with only 80nm Ag film coated is put from water (n_s=1.33) into alcohol (n_s=1.36). With the accuracy of wavelength measurement (20pm), the SPR-LPFG sensors are expected to have a sensitivity to detect ns (surroundings refractive index) with a change of ~5×10^-4. It is found that different thicknesses of different metal films show different measuring sensitivity. Through the comparison of the resonance wavelength obtained in air, water, alcohol, glycerin and their mixture solution, different sensitivities of the reflected SPR-LPFG sensors have been achieved. The proposed SPR-LPFG sensing scheme offers an efficient platform for achieving high performance fiber sensors for measuring ambient refractive index.