Based on the investigation data of pH, total alkalinity (TA), sea surface temperature (SST), salinity (S), dissolved oxygen (DO), dissolved inorganic carbon (DIC), Chl.a, etc. during four cruises from November 2012 to August 2013, the spatial and seasonal variations of dissolved inorganic carbon system parameters and aqueous pCO₂ were investigated in a large-scale mariculture area in Yantian Harbor,Sansha Bay. And the sea-air CO₂ flux was also evaluated. The results showed that the annual concentration of DIC, HCO₃^-, CO₃^2- and CO₂ was in the range of 955-1957.08,905.08-1848.13, 10.14-124.78 and 11.48-39.78 μmol/L, respectively. There were significant differences between seasons in concentrations of DIC, HCO₃^-, CO₃^2- and CO₂ (P<0.01). The annual value of aqueous pCO₂ was in the range of 391.27-1 200.49μatm, and sea-air CO₂ flux was in the range of 0.252-6.925 μmol/ (m²·d). These demonstrated that the Yantian Harbor was the weak source of atmospheric CO₂. There was significant difference for sea-air CO₂ between different sampling sites (P<0.05), and highly significant difference between different seasons (P<0.01). The sea-air CO₂ flux was the highest in autumn and spring, and was the lowest in summer. The sea-air CO₂ flux in winter was lower than that in autumn, but there was no significant difference with that in spring. The sea-air CO₂ flux was lower in the bay mouth than that in the upstream sea area in autumn, spring and winter. Distribution of pCO₂ and sea-air CO₂ flux were mainly controlled by hydrological conditions and biological uptake in Yantian Harbor. The large-scale seaweed aquaculture is helpful diffusion of CO₂ across the sea-air interface.