The morphology and wetting stability of nanofilms formed by AyByCz miktoarm star terpolymers were explored by many-body dissipative particle dynamics. The length ratio of C- to A-arm (w = z/y) ranges from 0.25 to 5. On nonselective substrates, the nanofilm displays morphology as the lamella at w < 0.5, various Archimedean tilings at 0.5 ≤ w < 3, and the alternating lamella at w = 3. The nanofilm becomes unstable at w = 5. While our findings of Archimedean tiling patterns [6.6.6], [8.8.4], and [12.6.4] are consistent with thin film experiments, [8.6.4; 8.6.6] and [10.6.4; 8.6.4] have not been reported. The wetting stability was determined by the final fates of thin films subject to disturbances, including (i) nucleation and growth, (ii) self-healing, and (iii) stable hole. The stability follows descending order: [6.6.6] > [8.6.4; 8.6.6] > [10.6.4; 8.6.4] > [8.8.4] > [12.6.4] > alternating lamella > lamella > alternating cylinder. On selective substrates with weaker or stronger attraction with C-arms, the defects formed by C-arms prevail for the former but the lamella morphology dominates for the latter.