<p>TC18 titanium alloy is a crucial material for the manufacture of aircraft landing gear, but its corrosion resistance is insufficient in marine salt spray, inland humid heat and other environments. Active Combustion High Velocity Air Fuel (HVAF) is an efficient thermal spraying process, which can prepare dense corrosion and wear-resistant coatings on the TC18 surface, effectively solving the problem of landing gear surface protection. Based on the computational fluid dynamics (CFD) method, a model for combustion reaction and discrete phase during HVAF spraying of WC-12Co powder was established in this work. The evolution law for flame flow temperature and velocity field and the correlation between particle size and particle flight characteristics were revealed. Based on Python scripting, the spray substrate with rough surface and spray particles with random spatial position and random particle size were established. The full-period 3D multi-particle random impact model was established based on CEL (Coupled Eulerian-Lagrangian). The evolution law of temperature, strain and stress fields for particle impacting on the smooth substrate and the rough substrate was revealed. The calculation results show that compared with the smooth surface in ideal conditions, the rough surface substrate inhibits the spray particles flattening motion. The bonding area between the substrate and particles increases, the particles equivalent plastic strain decreases, the substrate equivalent plastic strain increases. The substrate stress distribution is more uniform but the average stress value increases, and the warping resistance of coating is enhanced. The deposition process is more complex. This study is of great significance to reveal the mechanism of particle deposition on rough surfaces and effectively improve coating quality. And it provides a significant theoretical reference for particle deposition modeling on rough surfaces.</p>