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The quality of the environment could directly affect the production performance of pigs. Especially for weaned pigs, they have just undergone weaned stress and are very sensitive to external environment change. In order to evaluate the environmental conditions in the weaned pigs building in typical East China, and provide useful suggestions for pig barn structure design and the environment improvement, based on computational fluid dynamics (CFD) method, a three-dimensional steady state simulation was conducted on air speed, temperature, relative humidity and particle concentration distribution of a weaned pig building with negative pressure ventilation system and manure pit system. It was known from the CFD results that CFD could be a useful tool in analyzing the indoor environment in livestock house. When air was input to the pig house during winter days, the wind speeds in the region where pig was fed at z=0.2m could maintain within 0~0.2m/s, and most of them were below 0.1m/s. Also, the relative humidity remained at about 60%~70%. Its temperature was maintained within 26~34℃. In addition, the PM2.5, PM10 and TSP concentrations were kept in 0~0.1mg/m3, 0~0.7mg/m3 and 0~1.0mg/m3, respectively,in most area of pig house, which could meet the requirements of weaned pigs in winter according to environmental parameters and environmental management for intensive pig farms. Yet, at entrance of the units and some corners, there was still potential for optimization.