The purpose of this article is to design the optimum method of Propellant Management Device (PMD) of hydrazine fuel tank which used in zero-gravity conditions. To this end, numerical methods are used to analysis of the tank and the fuel behavior inside the tank with PMD to optimize system design parameters. Hence, Ansys version 17 software used to finalize modelling, analysis, meshing and consideration of fuel behavior in PMD by utilizing the Volume Of Fluid (VOF) method. Also Solid Works software version 2016 is used to primary PMD and tank modeling. Then, numerical simulation is performed to consider PMD's performance and to illustrate the capillary phenomenon for continues fuel transferring in zero-gravity conditions. The design variables in tank and PMD optimization respectively are: minimizing the tank weight to safety factor ratio; dimensional specifications of tank and PMD (height, diameter, length and width dimensions). The objectives of PMD optimization are to achieve maximum volumetric and mass flow rate values. On the other hands, to achieve the most desirable amount of fuel to PMD, that at the end of the time of simulation used by flow rates curves. Numerical analysis results that are obtained include: optimal system parameters related to the specifications of the tank with minimum weight and maximum safety factor and also optimal system parameters related to specifications of PMD with maximum performance of mass and volume flow rates in zero gravity. In conclusion, by comparing the existing systems with the optimal system parameters results will be verified.