The geomechanical stability of CO2-injected gas-hydrate-bearing sediments is dictated by the mechanical stability of CH4-CO2 heteroclathrate hydrates. Herein, tensile mechanical properties of CH4-CO2 heteroclathrate hydrates are for the first time explored using classical molecular dynamics simulations. It is revealed that CH4-CO2 heteroclathrate hydrates show apparent variations in mechanical properties with the ratio of CO2-to-CH4 and loading direction. As the stretching is perpendicular to the heterointerface, both the Young's modulus and Poisson's ratio follow the rule of mixture. Intriguingly, as the straining is parallel to the heterointerface, heteroclathrate hydrates exhibit higher Young's modulus over mechanically robust CH4 hydrate, originating from nonuniform Poisson effect induced transverse tension in the CO2 hydrate region. Depending on the loading direction, heteroclathrate hydrates are able to show brittle or ductile fracture behavior, and fracture initiates via the dissociation of water cages at the weak CO2 hydrate region instead of heterointerfaces. This study provides a key database of mechanical properties of CO2 injected CH4 hydrates and molecular insights into the mechanical stability of CO2 -contained CH4 hydrate under reservoir deformation. The formation of heteroclathrate hydrates occurs when carbon dioxide replaces part of the methane molecules in the clathrate hydrate. Also, it has unusual mechanical properties.