Abstarct: The aimed of this research is studies about mechanism and performance of gorgan bay and miankaleh sand spit with field and numerical studies and suggested the best way for reborn gorgan bay in time of closure inlet. Miankaleh sand spit and gorgan inlet always are changing due hydrodynamic factors. Different factors such as wind, wave, current, storm, area slope and sea level change are effective in this transformation, which each factor or interaction each factor left behind some physical evidence in the beach. In this research used field studies along with numerical modeling by mike 21 (HYDRODINAMIC, HD. SPECTRAL WAVE, SW. SEDIMENT TRANSPORT, ST). According to result of this research, miankaleh coasts are type of dissipative coasts and wave energy and current speed reduced from west to east and most grain detemeter is 0.106mm and west zone of miankaleh coasts has erosional properties and the east zone has depositional properties. From west to east of studies area, results shows increases intensity sensitively of coasts toward sea level changes. Most edd height formed due storm in east coasts is about 40 centimeter and can bring up bay level to 15-20 centimeter. The volume of depositional sediments in gorgan inlet formed from sea level changes in Caspian Sea (field studies) and ashooradeh channel stand due low wave energy. Directional average of current in one year in out of bay is from west to east and in the bay is acts as counter clockwise. The rate of sediment discharge in gorgan inlet is 0.001 cubic meter per second per 1 meter and rate of bed level changes in inlet is less than 1 centimeter per day while rate of sediment discharge in miankaleh beach is less than 0.00002 cubic meters per second per 1 meter. Gorgan inlet closure due 3 scenario, first scenario is reduced sea level until inlet closure. Second is acts of reduce sea level with big storm and the third scenario is acts sea level rise and sea level fall after together. According to studies on research in this field , offer solutions such as construction of protective structures and dredging the channel for aim of keep connected water bay to sea is inefficiently recommended and the best solution for keep the bay safe is construction an artificial channel in west zone of miankaleh coasts recommended and allocated.