In this research, the effect of Trypsin and SDS on Portunus trituberculats was analyzed. Phenoloxdase (PO) of plasma and hemocytely supernatan (HLS) were measured as well as the Kinetic curve of PO activity of Trypsin and SDS conducted on plasma and HLS; Analysis the prophenol-oxidase activated system (ProPO-AS) existing position and immune mechanism of Portunus trituberculatus. The results showed that PO activety of HLS (9.93U±1.03U) is higher than plams (0.80U±0.04U);the effect of Trypsin conducted on plasma and HLS was not significant were: 0.91U±0.07U and9.06U±3.65U; the effect of SDS conducted on plasma and HLS was obvious were 0.96U±0.03U and 71.12U±14.25U.ProPO-AS of Portunus trituberculatusexist in hemocytely, it participate the immune response through different paths: Trypsin through the multi-stage enzyme-linked immunosorbent reaction to oxidize ProPO to PO while SDS active PO by change the structure of ProPO. The efficiency of SDS active ProPO-AS is significanly higher than Trypsin.