The sea-to-air flux of dimethylsulfide (DMS) is potentially an important determinant of regional climate. A nitrogen-based ecosystem model with unidirectional coupling to a sulfur-based biochemical model is used to simulate DMS flux in the Eastern China Marginal Seas (ECMS) (25°N-40°N, 120°E-130°E) during year 2011. Monthly mean of meteorological forcings (sea surface temperature (SST), wind speed (WIND), cloud cover (CLD) and mixed layer depth (MLD)) are used to force the model. A parametric sensitivity analysis is conducted to identify the critical model parameters. A genetic algorithm technique is then used to calibrate the most sensitive model parameters. The simulation results show that phytoplankton biomass (CHL), DMS, its precursor dimethylsulfoniopropionate (DMSP) and DMS sea-air flux all reach their seasonal maxima in early April with smaller peaks in June and August. Spatial mean DMS ranges from 2.1–10.8 nM with a mean value of 3.8 nM; spatial mean DMS flux ranges from 2.5–10.4 umole/m2/day with a mean value of 5.43 μmole/m2/day. The validation test results indicate that our simulation results are closer to the field data comparing to calculation results from Simó's formula. The high simulated DMS sea-air flux on the coastal shelf suggest that the DMS cycle in the ECMS is potentially important to the regional climate and should not be ignored.