When a droplet resting on a surface, its shape can be nonspherical or asymmetrical due to the surface heterogeneity, and surface temperature and evaporation flux may distribute asymmetrically during evaporation process thereafter. The evaporation of a nonspherical sessile droplet was simulated regarding heat and mass transfer process in this paper, which consists of part of a spherical cap and part of an ellipsoidal cap. Due to its asymmetrical shape, the surface temperature, saturated vapor concentration and evaporation flux distribute asymmetrically. The average surface temperature and average saturated vapor concentration are higher at ellipsoid side, but the average evaporation flux is higher at sphere side. Furthermore, due to the bigger curvature radius at ellipsoid side, the droplet evaporates faster at this side.