Abstract: Ventilation is one of the most critical influencing factors in the homogeneous and efficient decomposition of organic matter during composting. Among them, the supplied air velocity of the perforation holes can dominate the airflow velocity in the pipe and the static pressure perpendicular to the pipe wall. Furthermore, the airflow direction from these perforation holes can often deviate towards the central axis of the pipe, leading to a ventilation-deficient zone in the proximal inlet area. The airflow direction can also be attributed to the relatively higher airflow velocity near the inlet. However, the insufficient ventilation can cause the low efficiency of the composting. In this study, the deflectors (0.75, 1, and 1.25 cm in height) were introduced behind the first perforated hole along the airflow direction. Computational Fluid Dynamics (CFD) analysis was employed to optimize the deflector height. A systematic investigation was also made on the impacts on the manure composting efficiency and microbial community dynamics. Results demonstrated that the optimal deflectors effectively mitigated the ventilation-deficient zone near the inlet. The height of the deflectors also dominated the airflow uniformity. Specifically, the deflector with a height of 0.75, 1, and 1.25 cm increased the average airflow velocity by 10.8%, 34%, and 34.2%, respectively, compared with the without deflector. In addition, there was no significant increase in the airflow speed with 1 and 1.25 cm deflectors. Finally, the height of the deflector was selected as 1cm, according to the cost and convenience. Two experiments were conducted to take the deflector-installed (1 cm) ventilation pipe as the treatment group (T), and the pipe without deflectors as the control group (CK). Compared with the CK, the T exhibited a 2.1°C temperature increase during the thermophilic phase. While there was the decrease of 5.5%, 2.35%, 0.15 mS/cm, 1, 0.1, 35.76 mg/kg, 20.94% in the moisture content, the volatile solids (VS), the electrical conductivity (EC), the carbon-nitrogen ratio (C/N), the pH value (pH), the ammonium nitrogen (NH₄⁺-N), and the germination index (GI) at maturation period, respectively. High-throughput sequencing revealed that the deflector significantly enhanced the diversity of the microbial community. The airflow increased near the inlet, indicating the increase in the Chao 1 and Shannon index. At the level of the microbial phylum, especially during the thermophilic phase, the degradation of the macromolecular organic substances (such as the quick-acting carbon source substances) was promoted to increase the relative abundance of Firmicutes. The degradation of cellulose and lignin was promoted to increase the relative abundance of Actinomycetes and Proteobacteria in the cooling and maturing phases. Redundancy analysis indicated the positive correlations between Firmicutes and Temperature, as well as Actinobacteria/Proteobacteria/Bacteroidota and GI. While there was a negative correlation with the VS, C/N, NH4+-N. At the level of microbial genus. Especially in the thermophilic phase, the carbon consumption and heat release in organic matter were intensified to increase the relative abundance of Thermobifida and Bacillus. Redundancy analysis indicated the positive correlations between Thermobifida/Bacillus and temperature, while the negative with C/N ratio. Saccharomonospora/Parapedobacter showed a positive correlation with the GI, while a negative with the VS. Therefore, the deflector can be expected to increase the airflow volume near the inlet, thus promoting the degradation and maturity of the composting pile. This finding can provide the technical support to optimize the ventilation pipe during manure composting.