Surface plasmon resonance (SPR) is a kind of optical detecting method and popular to use in biosensor recent years. SPR biosensor has several advantages such as label-free and high sensitivity. Many biomolecules have special selectivity to bind with another biomolecule in complex biological media. Efficiency of binding can be improved by using micro-channel. In this thesis , we use a home-made SPR system and find its sensitivity and resolution . Compare the difference of conducing immunoassay in micro-channel and on gold thin film. Then, we find the good condition by different flow rate and channel size. At last, we detect the cancer maker protein ,prostate–specific antigen (PSA), and mix PSA in serum to simulation real exsanguinate test.