Abstract: Abstract: The environment inside the livestock building plays a vital role in animal growing and livestock production efficiency. The analysis of the airflow field and the temperature field can clarify the real situation of the environment and find flaws caused by the design of ventilation system and building structure, thus helps improve the building design and increase production efficiency. In this study, we used computational fluid dynamics (CFD) to simulate the airflow field and the temperature field in a Specific Pathogen Free Swine (SPF) boar building of Beijing breeding swine center, which was ventilated with mechanical evaporative cooling system. The boar building had 47 m length, 14.8 m width and 1.2 m height with a deep manure pit in 0.8 m depth. There were four rows and five aisles placed inside. Farrowing crates were used for breeding boars. Each farrowing crate was size in 2.3 m×0.8 m×1.2 m. The floor of the building was slatted in a length of 12 cm with a gap of 2 cm width. One end wall was equipped with the evaporative pads and the other one equipped with four 1.25 m ventilation fans and two 0.9 m ventilation fans. Manure pits ventilation system was equipped with four exhaust fans for extracting harmful gases and odors from the building. A standard k-? model was built by simplifying slatted floor to porous media for approximating the real situation inside the building. The simulations of temperature field and airflow field in terms of the model were made for both the boar building with and without boars. Measurements experiments were implemented from 21st to 27th June in 2012. Forty five measurement points were dispersed uniformly in the building at three different heights, 0.60 m, 1.2 m and 1.7 m above the slatted floor. 6 points at different locations at 0.25 m depth underneath the floor were added to measurements. For each measurement point, we collected both air velocities and temperatures, using a temperature and humidity instrument (Testo608-H1) and an anemometer (Testo-405), respectively. Measurements were implemented from 12:00 to 14:00. The air velocities also were measured at evaporative pads, ceiling inlets, ventilation fans. The temperatures of walls, floors and ceiling were collected by a wall thermometer during this time period as well. Temperature and airflow values derived from practical measurements in the building without boars inside were compared with the values form the simulated model. After that, this model was used to simulate the boar building with boars to analyze and observe the reasonability. For the unloaded building, results showed that values at the measurement points from the airflow field were very approximate to those from the experimental measurements, the relative errors of airflow ranged from 0.25% to 30.8%. Among 45 measurement points above the slatted floor, the relative errors of three values were over 20% and 14 values over 10%. Likewise, the difference between the simulated values and measurement values were very small in temperature. The maximum absolute error between the simulated values from the temperature field and the practical values was 0.48 K, the even absolute error and the even relative error were 0.11 K and 0.5%, respectively. Furthermore, the simulations for loaded boar building showed the reasonability both in increasing overall temperature and reducing airspeed behind each boar. Meanwhile wave movements of the airflow under the slatted floor were observed to signify the possibility of the noxious gas drifting into the animal occupied zone that could harm boars. The study of the simulations in boar building can improve the ventilation system of the building and thus protecting boars from noxious gas and high temperatures effectively. It also helped model and analyze swine buildings mounted with prevalent slatted floor and mechanical ventilation system. It also provided the theoretical basis for remaking and constructing the livestock building.