Free-living Porphyra haitanensis conchocelis was cultured under continual light,then it was treated with Van,DIDS and SITS,the inhibitors of inorganic carbon utilization,to study the mechanism of inorganic carbon utilization in the conchocelis.The results indicate that Van inhibits the utilization of inorganic carbon most,with a rate of 71.3%,and the rates of DIDS and SITS are relatively lower,42% and 35.5% respectively.The inhibition rate of Az is 25.3%,which indicates the external CA is not an important part of its inorganic carbon uptake.A complementary conclusion is that the main part of inorganic carbon absorption in P.haitanensis conchocelis is through active transport of HCO3^- and CO2.