Sterilizing tunnel oven is the key equipment to realize aseptic production in the pharmaceutical industry. The uniformity of air flow is the key index of sterilizing effect, which is influenced mainly by the structure of sterilizing oven. Therefore, the rational design of oven internal structure is an important way to achieve uniform airflow. However, there are few researches on the uniformity of air flow in the sterilizing oven. A hot air circulation tunnel oven was taken as the research object, the CFD numerical simulation method was used to study the internal temperature and flow field of the oven, and six optimized structures were proposed according to the internal flow condition of the tunnel oven, and the airflow distribution characteristics of different optimized structures were compared and analyzed. The results showed that the local temperature difference at the outlet of the oven was less than 1 K, the temperature distribution was relatively uniform. The air velocity distribution was the main factor affecting the drying quality, while the high-speed airflow cannot spread evenly because of the small space of the fan cover. The flow distribution of outlet was extremely uneven under the original structure, and there was a local high-speed region at the corner of the outlet surface. The maximum speed was 3.48 m/s, the average speed was 0.94 m/s, and the relative root mean square of airflow velocity was 0.73. Compared with the original structure, the maximum outlet velocities of the six optimized structures were significantly reduced. The percentages of the optimum velocity range increased in different degrees and the airflow uniformity was improved. While the elbow structure with three baffles had the lowest relative root mean square value of the outlet, the maximum speed decreased by 51.4%, the percentage of the optimum speed area increased to 75.17%, and the rectification effect was the most obvious. At the same time, after setting three baffles in the elbow, setting baffles in the fan cover had little effect on improving airflow uniformity, which provided a reference for improving airflow uniformity of the hot air circulation tunnel oven.