The mechanical properties of polyglycolic acid (PGA) with different contents of water weight fractions (1.7%, 2.9%, and 5%) were investigated by molecular dynamics (MD) simulation through the tensile test.The crystallinity digress variation on the water content was also investigated by the XRD profiles.The Youngs modulus, mechanical strength, and fracture mechanism of all PGA/water systems were drawn by the corresponding stress-strain profiles.Furthermore, the water diffusion behaviors within PGA matrix before and after the tension test were also studied.The water diffusion coefficients were derived from the mean square displacements of all water molecules within the PGA matrix.