The effect of particle sedimentation on the evaporation rate of nanofluid droplets on a heated substrate is studied numerically. A two-dimension model of droplet evaporation and deposition using Arbitrary Lagrangian-Eulerian (ALE) method is developed, considering evaporation cooling, two-phase heat transfer, mass diffusion, nanoparticle transport and free surface evolution. The effects of temperature and particle concentration distribution on the total and local evaporation rate of millimeter-sized sessile nanofluid droplets with varying substrate temperature are numerically analyzed. It is shown that the nanoparticle concentration nearby the droplet edge is much higher than that nearby droplet center, and also the sedimentation at droplet edge is much more than that at droplet center. The non-uniform nanoparticle concentration inside droplets leads to a greater temperature difference along the free surface.