A robustness optimization of SRAM dynamic stability at nano-scale is developed in this paper by zonotope-based reachability analysis. A backward Euler method is developed to efficiently perform reachability analysis by zonotope to deal with multiple device parameters with tuning ranges. Moreover, a sensitivity calculation of zonotope is developed to optimize safety distance by simultaneously tuning multiple SRAM device parameters without multiple repeated computations. As such, sequential robustness optimizations can be performed such that the optimized SRAM designs can depart from unsafe region but converge into safe region. The proposed method is implemented inside a SPICE-like simulator. As shown by numerical experiments, the proposed method can achieve 600× speedup on average compared to the traditional verification method by Monte-Carlo under the similar accuracy. In addition, compared to the traditional small-signal based sensitivity optimization, the proposed method can converge faster with high accuracy.