Droplet runback on a solid surface driven by gas flow is commonly seen in aeronautical engineering, such as in aircraft icing that adversely affects flight safety, and in water accumulation inside a fuel cell that reduces its energy efficiency. The authors so far have been developing a numerical simulation method that combines liquid calculation by the moving particle simulation (MPS) method and gas calculation by the finite volume method to solve droplet dynamics that interact with gas flow. The particle and grid methods are coupled by the immersed boundary method. A coarse grid can be used to lower computational cost while using fine particles to properly capture droplet deformation. The method has been evaluated by simulating droplet breakup and liquid jet atomization. This time, the method was applied to droplet runback. An experiment that measured the critical air velocity for droplet motion was simulated. Droplet runback at the critical air velocity was predicted. The computation time for one case using an ordinary workstation was 3 minutes. Comparisons between aerodynamic force and surface tension/wettability models applied to the MPS method, as well as evaluations that cover various surface wettability and airflow conditions, will be presented at the conference. The present method, capable of simulating droplet runback at low cost, will contribute to understanding the physics, evaluating the negative effects, and finding ways to effectively control droplet runback and liquid accumulation, which will lead to improving safety and efficiency of aviation.