Water Renewal Time is an important index for determines pen culture fish farms location in the marine ecosystem.Thetime scalerepresents,the time it takesto replace63 percent of the water in awater bodywithfresh waterisimportedfromneighboringareas such as spans, strait, river and channels.In this research, in order to investigate the Renewal Time in the Gorgan Bay, two modules from three dimensional MIKE3 model including Hydrodynamic and Advection-Dispersion were coupled as real time.Modeling was performed on unstructured triangular meshes and three layers with one meterThickness with considering factors such as wind speed, wind direction, rivers input, precipitation, evaporation and water fluctuations in spans of Ashooradeh-BandareTorkman.In order to determining of start time modeling, water level fluctuations were investigated in the spans of Gorgan Bay. Accordingly, the best time for consideration of calculations, the trend beginning of water level risingwas selected in the Gorgan Bay.Mixed model of smagorinsky in horizontal plan and  in vertical direction was used for turbulence modeling.Local Renewal Time calculated in 31 areas and meshes with 16.8 km² in the Gorgan Bay.The modeling results represented, local Renewal Time strongly influenced by prevailing hydrodynamic regime in the Gorgan Bay and this time index increasing by moving east to west.Integral Renewal Time was calculated 50.25 days.Renewal Time was similarity in vertical direction and same layer corresponding to each cell.Maximum amount of this time scaling was 65.3 days in 31th area located at the western end of the lagoon Miankaleh and the minimum was 1.5 days in first area and neighboring by Ashooradeh-BandareTorkmanopenings.In based of local Water Renewal Time, the best places in order to building and development of fish farms are the extreme of north-eastern and eastern parts of the Gorgan Bay in zones 1 to 6.