The horizontal optical testing system with large aperture and long focal length is extremely susceptible to the airflow disturbance, which will cause random dynamic changes in time and space of multiple physical quantities in the optical path, such as temperature, velocity and pressure. In particular, the spatial heterogeneity and temporal stability of temperature will directly affect the dynamic change of air refractive index, resulting in the degradation of the point spread function, the tilt of the wavefront and the change of the wavefront over time. In order to suppress the influence of airflow disturbance on the testing optical path and improve the testing accuracy, based on the Computational Fluid Dynamics (CFD), a forced convection method was proposed to improve the uniformity of the indoor temperature field, which can be used to determine the array mode and number of fans. The Peak to Valley (PV) of the temperature was adopted and the concept of maximum optical path differences was introduced to comprehensively evaluate the uniformity of the indoor temperature field. Verified by several groups of experiments, the forced convection scheme reduces the standard deviation of the astigmatism coefficient from $0.146 \lambda $ to $ 0.026\;3 \lambda\;(\lambda=632.8\; \mathrm{nm}) $, which significantly improves the uniformity and stability of the indoor temperature field, greatly reduces the optical testing error, and improves the testing accuracy. It provides a reference for ensuring the optical testing accuracy of the optical testing system with long optical path and large aperture in the future.