Abstract： The code of Fortran and Fluent were selected to study thermophoretic deposition of particles in rectangular narrow channel by considering the humidity ratio of air. Meanwhile, an approach of using the code of Fluent to calculate the thermophoretic deposition rate was proposed, and verified by the results of Fortran programming. The results show that the thermophoretic deposition rate increases with the increase of humidity ratio of air. When the humidity ratio is invariant, the thermophoretic deposition rate increases with the decrease of particle size and pressure, and with the increase of temperature gradient. In addition,different thermal properties of different particles lead to differences in thermophoretic deposition rate. Although the method proposed could reflect the law that the thermophoretic deposition rate changes with the humidity ratio, particle size and variation of the pressure, the calculation result is small. Measures  such as improving the humidity ratio of gas and reducing the pressure in the pipe can be taken to increase the deposition rate of fine particles.