Abstract: In order to optimize the ocean transportation capacity of liquefied ethane carriers, a method to improve the loading limit of cargo tanks in liquefied ethane carriers was researched according to the basic requirements on the loading limit of cargo tank in liquefied gas carrier and properties of liquefied ethane. In the method, the loading limit of cargo tank in liquefied ethane carrier is improved by increasing the relative density and filling limit of cargo under the reference temperature. The effects of BOG recovery methods on the ethane density control were analyzed by combining the actual data of liquefied ethane carrier with its theoretical calculation. In order to make the filling limit of main tank up to 99.5%, a gas chamber was set at the top of the tank and a pressure release valve was installed at the top of the gas chamber. In addition, the effects on the loading limit from level measurement, temperature measurement, start pressure setting of reliquefaction unit, response cycle of emergency shutdown, tank size and other modification margin factors were investigated. Thus, the method to improve the loading limit while satisfying the constraint conditions was developed. It is shown that the relative density and filling limit of liquefied ethane under reference temperature are increased by 6.67%-8.89% and 1.5%, respectively, and this method can be applied and popularized to the storage and transportation of other liquefied ethane carriers.