Heterogeneous condensation of water vapor on particle surfaces is a highly valuable industrial pretreatment technique for dust removal. Heterogeneous condensation of water vapor on particle surfaces can significantly improve the efficiency of dust removal. To study the dynamic behavior of droplets on the surfaces of particle during the process of heterogeneous condensation, the environmental scanning electron microscope (ESEM) is employed for visual observation of the heterogeneous condensation process of water vapor on particle surfaces. The evolution process of droplet mode is studied, and the contribution of line tension to the Gibbs free energy of the system during the condensation process and the influence of particle size and contact angle on line tension are analyzed. The results indicate that particles first nucleate to form a critical embryo droplet. This embryo droplet continues to grow and rapidly spreads to the equator of the particle. The droplet then remains on the equator, undergoing continuous condensation and growth, gradually transitioning to crossing the equator. With increasing condensation time, the droplet gradually envelops the particle. Once the particle is completely enveloped, the heterogeneous condensation transforms into homogeneous condensation and continuous growth. The entire condensation process can be divided into five modes: nucleation, diffusion, transition, encapsulation, and growth. The line tension of the five modes is analyzed, and it is found that when the droplet is in the upper hemisphere of the particle, the closer it is to the equatorial line, the greater the contribution of the line tension to the Gibbs free energy change of the system, which promotes its movement towards the equatorial line, and when it is in the lower hemisphere, it promotes its encapsulation of the particle. The effects of particle size and contact angle on the line tension are numerically studied, and it is found that the line tension increased with the increase of particle size. The influence of the intrinsic contact angle of the particle on the line tension is small, but the bigger the difference between the particle and the apparent contact angle, the greater the line tension.