Abstract: The particulate mixing chamber is a specialized device designed to control concentration and achieve uniform mixing. This equipment, when used in conjunction with standard particulate devices, enables the calibration of instruments measuring particulate mass concentration. Therefore, ensuring the uniformity and stability of particulate concentration within the mixing chamber is crucial for metrological calibration. This study employs a combination of computational fluid dynamics (CFD) simulation and experimental validation to identify three factors affecting the mixing characteristics of the particulate mixing chamber: the height of the dilution section, the height of the middle section, and the height of the diffusion section. Orthogonal experiments were conducted to optimize these parameters. The optimal mixing effect was achieved with a dilution section height of 50 mm, a middle section height of 50 mm, and a diffusion section height of 100 mm. Under these conditions, the mixing performance meets the calibration requirements for most commercially available PM₁₀, PM_2.5, and other environmental air particulate mass concentration testing instruments, as well as low-concentration dust analyzers.