Abstract: Abstract: Although fan-pad tunnel ventilation evaporative cooling system is energy ef?cient and environmental friendly, which consists of a fan on one sidewall and a pad on the other sidewall, is rarely applied in beef cattle barn. The cooling efficiency of the fan-pad evaporative system can reach more than 85%. With the advent of the computer age, computational fluid dynamics (CFD) technology is widely used to predict the movement of air or other environmental factors. In order to study the effects of fan-pad evaporative cooling system applied in beef cattle barn in summer, the CFD technique was used to simulate airflow and temperature distribution inside the barn, based on the environmental index measurement, to improve and optimize the effect of the system. The barn building was 54 m long, 12 m wide and 4.2 m at height, window sill height was 1.5 m, and electric curtain was 2.7 m high. There were 58 beef cattle averaged 500 kg of weight included in the study. In the simulation, the beef cattle were introduced into the model according to equal proportion, a realizable k-ε model was built, and the SIMPLE (semi-implicit method for pressure linked equation) was used for the pressure velocity coupling. Measurements experiments were implemented from July to August, 2014. Seventy-five measurement points were dispersed uniformly in the building at 3 different heights as 0.6, 1.2 and 1.8 m above the bed floor, which respectively represented the lying down area, activity area and head above. For each measurement point, both air velocities and temperatures were recorded, using a three-dimensional anemometer and a temperature and humidity instrument respectively. Measurements were conducted at 10:00, 14:00 and 18:00. These measurement indices were used for the validation of the anastomosis. Meanwhile, the velocity and the temperature of fan and pad were also measured. The temperatures of walls, floors and ceiling were recorded by thermal infrared imager (Fluke Ti400), which were used for modeling. After the simulation was completed, the results showed that the temperature distribution was uniform, but affected by the beef cattle in the barn, and the air distribution was uneven, the high air velocity area was mainly concentrated in the roof and feeding aisle with 0.9-1.2 m/s, and the wind speed of beef cattle activity area was less than 0.6 m/s, which could not meet the feeding standards. The CFD model was validated via comparison with the field experimental results at the same locations by the sensors. Comparison between simulations and measurements showed that the relative errors were 0.16%-94.41% after 5 outlier elimination, the average relative errors were 34.53%. For the 45 temperature measuring points, the relative errors were 0.09%-10.74%, the average relative error was 4.71%, which indicated that there was a good fit between field measurement and numerical simulation. Without changing the envelope and indoor barn structure, a guide plate was arranged inside, making the uniformity of the temperature and airflow field in the room improved significantly and the cooling effects more significant. Therefore, this study can provide references for the optimization design and environment regulation of fan-pad evaporative cooling system of beef cattle barn.