The modelling of type-A tanks of a liquefied gas carrier is complicated and highly coupled with the principal dimension, hull lines and target cabin capacity. A parametric modelling based subdivision optimization design method for the type-A tank of a liquefied gas carrier (Parametric Optimization Method for Subdivision of type-A tanks, POMSA) has been proposed to improve the efficiency of the overall optimization design of the type-A tank of a liquefied gas carrier. The key technology of this method is the parametric modeling based on the NAPA platform.The typical midsection shape, the longitudinal position of the main transverse bulkhead and the angle of the inner hull are parametrically modelled and regarded as design variables in this paper.The principal dimension, hull lines and the initial general arrangement are taken as input. The requirements of the tank location from IGC, the minimum side length of the tank from the construction process, the target cabin capacity, the propeller immersion and the vision requirement of the ballast water are used as constraints for POMSA. The maximum cabin capacity is taken as the optimization design objective. The optimization model is solved by the optimization mathematical modelling of an exploratory global optimization algorithm (Non-dominated Sorting Genetic Algorithm-II, NSGA-II) together with a local fast convergence optimization algorithm (Hooke-Jeeves direct search method). It is proved that the optimization iteration of this method is efficient, which will facilitate the fast response at the early design stage of the overall design.