In order to study the effects of external particles on the supersonic condensation process of natural gas, an experimental system to test the supersonic condensation efficiency is set up and the models for spontaneous (homogeneous) and heterogeneous condensation of natural gas are established. Vapor and liquid flow control equations are derived based on the two-fluid Euler model, and internally consistent classical theory and Gyarmathy's model are used to calculate the droplet nucleation rate and growth rate respectively. The results show that the due to the inhomogeneous condensation caused by the external particles, the measured droplet radius is larger, but the number of droplets is smaller in the experiment. With the increase of external particle concentration, the spontaneous condensation is gradually suppressed and heterogeneous nucleation is becoming more and more obvious. The increase of external particles concentration is beneficial to the condensation and the total humidity becomes larger, but when the external particle concentration increases to a certain value, the promotion effect is limited. In addition, other parameters such as the radius of particles also have influence on the heterogeneous condensing flow of natural gas. (C) 2018 Elsevier B.V. All rights reserved.