For the problem of uneven distribution of gas hydrate synthesized in porous media, a new method for obtaining hydrate samples in porous media by microwave heating was proposed and a microwave heating apparatus was designed for this method. Based on the electromagnetic theory and the influencing factors of microwave heating uniformity, the adjustable multi-feeding microwave heating system was created. Numerical simulation and relevant heating test were made to analyze the effects of relative positions of the waveguides and specimen on apparatus heating uniformity, by which the feasibility of the apparatus to prepare gas hydrate synthesis was discussed. The results show that the heating uniformity is greatly affected by the variation of distance between the waveguides and specimen and it gets better with distance significantly. The consequence of numerical simulation is consistent with the result of experiment. The heating uniformity of the apparatus is less affected by heating time and the apparatus can meet the requirement of hydrates synthesis in uniformity，and its design may provide certain reference significance for the design of testing devices with some requirements in heating uniformity.