Abstract: In order to study the natural deposition behavior of submicron aerosols at a small steam condensation rate, an experimental platform was built and the related experimental research was carried out in this paper. In the process of the experiment, the self-developed sampling pretreatment system was used to carry out the aerosol sampling analysis in the high temperature and high humidity environment. The gravity sedimentation mechanism is one of the most common removal mechanisms in natural deposition. Several gravity sedimentation experiments were carried out first, and the experiments were used as the basis for other experiments. Next, the natural deposition experiment of sub-micron aerosol was carried out at a small steam condensation rate by adjusting the steam condensation rate before distributing the aerosol. Based on the gravity sedimentation data with the same thermal parameters, the attenuation constants under the action of thermophoresis and diffusiophoresis were obtained. The results show that when there is steam in the working medium, the gravity removal effect of submicron aerosol is better than that of pure air under the same thermal conditions. The proportion of steam can promote the gravity settlement. The pressure has inhibitory effect on gravity settlement. And with the increase of pressure, the increase of steam share has a more significant effect on the increase of gravity removal rate. In the natural removal process of submicron aerosols, the proportion of removal by diffusiophoresis and thermophoresis mechanisms increase with steam condensation rate, accounting for more than 90%. Under the condition of low vapor condensation, the contribution of diffusiophoresis is great, followed by gravity deposition, and thermophoretic deposition can be ignored to a certain extent. When the steam density is low, the diffusiophoresis sedimentation rate is in good agreement with the S/W model. When the steam density increases, the experimental sedimentation rate is higher than the calculation result of the S/W model, and relevant corrections have been made. Under the same thermal parameters, the diffusiophoresis sedimentation rate of NaCl is much higher than that of TiO2, and much larger than the prediction results of the three current diffusiophoresis models.