Fiber-coupling surface Plasmon resonance sensor has attractive advantages of information transmission such as small volume, anti-electric magnetic field interference, and online real-time remote detection. In order to improve the performance of the sensor, the effect of the residual fiber thickness and the silver film thickness to the sensitivity of the sensor and the depth of the resonance peaks and full width ar half maximum (FWHM) are analyzed respectively. The results show that the increasing fiber residual thickness weakens the SPR phenomenon, and that the increasing silver film thickness widens the resonance peak, while the sensitivity of the sensor does not change monotonously. Through the integration of refractive index sensing sensitivity and full width at half maximum, figure of merit is presented and regarded as the optimized objective. The optimal design is achieved in the case of the fiber residual thickness for 66. 5 µm, and the silver film thickness for 50 nm. The optimized design with the figure of merit of 98. 67 is expected to be applied in the bio-chemical sensing and analysis.