The structure of packing material was designed for waste gas purification system of pig house, and structural mechanical properties and purification space requirements were both considered in the designing process. The packing material was regarded as a kind of periodic structure, and the topology of the cell structure was optimized based on a multi-objective optimization method that combined the reverse homogenization method and the parametric level set method. In the optimization design, the maximum effective bulk modulus and the maximum effective permeability of the packing material were taken as the optimization objectives, and the effective porosity was taken as the constraint. The maximum values of effective bulk modulus and effective permeability coefficient were obtained by Hashin-Shtrikman property boundary. Pareto optimization method was used to achieve the Pareto optimal solution satisfying the multi-objective conditions. Three numerical examples achieved structural designs of the packing material under different porosities, and the feasibility and correctness of the proposed design method was verified by experiments. The experimental data showed that the pressure difference between front and rear of the packing material was inversely proportional to the porosity of the packing structure and directly proportional to the inlet wind speed. When the porosities of packing material were 80%, 85% and 90%, the average ammonia removal efficiencies were 66%, 62% and 58%, respectively. The research result can provide a reference for the design of the packing structure for waste gas purification system, and the proper packing material can be selected according to the actual requirement of wind resistance and purification efficiency in different pig houses.