Twin boundaries (TBs) were identified to show conflicting positive/negative effects on the physical properties of CH3NH3PbI3 perovskite, but their roles on the mechanical properties are pending. Herein, tensile characteristics of a variety of TB-dominated bicrystalline CH3NH3PbI3 perovskites are explored using molecular simulations. TB-contained CH3NH3PbI3 are classified into four types from their tensile ductile detwinning characteristics. Type I is characterized by smooth loading flow stressstrain responses, originating from relatively uniform stress distribution induced gradual amorphization at TB region. Types II and III are represented by sudden drop of loading stresses but then distinct ductile flow stress-strain curves, resulting from limited and large-area amorphizations of TB-involved structures, respectively. However, Type IV is highlighted by double apparent peaks in the loading curve followed by ductile flow response, coming from stress-concentration of localization-to-globalization at TB structure, as well as amorphization. This study provides critical insights into mechanics of CH3NH3PbI3 perovskites, and offers that TB engineering is a promising strategy to design mechanically robust hybrid organic-inorganic perovskites-based device systems
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