Surface plasmon resonance (SPR) biosensor is a powerful tool for biomolecular interaction analysis in proteomics research and drug discovery. But when it is used to analyze small molecules, the sensitivity still needs enhancement. Phase detection is a potential solution, for phase changes more abruptly than intensity when SPR is excited. An SPR system is developed based on spatial modulation phase detection (SMPD). In this system, collimated monochromatic light is used to excite SPR, and the phase of the reflected light is spatially modulated to generate an interference pattern. By processing the interference pattern by certain algorithms, instantaneous phase distribution of the whole sensing area can be obtained. Continuously detecting the phase change, the whole process of biomolecular interaction can be recorded in the form of phase change, based on which we can make kinetic analysis and get kinetic parameters. Antibody array chip is tested by this system. Experimental results indicate that this technique is capable of array detection and is more sensitive than intensity detection.