The sensitivity and dynamic range are main performance parameters of a Surface Plasmon Resonance(SPR) biosensor with phase modulation. In this paper, the main effect factors on sensitivity and dynamic range of the sensor were analyzed, and the influence of nonlinear change of phase difference on the results of real-time monitoring biological reaction was analyzed. A high resolution SPR system based on a Mach-Zehnder configuration was set up. The phase difference curves of a series gold membrane thicknesses and incident angles were simulated by matlab software, and the effect of several factors on the resolution and dynamic range were evaluated. In addition, the real-time monitoring of binding reaction between Bovine Serum Albumin(BSA) and BSA antibodies was also demonstrated. Obtainecl results show that the influence of membrane thickness is significant and nonlinear, but the incident angle shows little effect on the resolution and dynamic range. The influence of narrow dynamic range on biology reaction measurement can be minimized by optimizing some parameters, such as membrane thickness, incident angle and reactants concentration. Experimental results show that the sensitivity and dynamic range can be optimized by adjusting gold membrane thicknesses. This paper analyzed several influence factors of the sensitivity and dynamic range of phase modulation SPR biosensors. For a light source with 633 nm wavelength, the most optimal membrane thickness is 48 nm when the reaction between BSA and its antibody is measured. In this situation, the dynamic range is 0.013 6RIU and the sensitivity is 6.67×10-7RIU/0.01°.