Collagen represents the most abundant protein in the human body and plays an important role in connective tissues. Here, molecular dynamics simulation was performed to assess tension of a single collagen molecule, and stress-strain curves were obtained. In total, two regions (termed regions I and II) in the curve were displayed. In region I, as the pulling velocity increased from $0.5{AA}/ps$ to $5{AA}/ps$, the effective elastic modulus increased from 18.613 GPa to 27.632 GPa when water surrounded a single collagen molecule and increased from 15.308 GPa to 17.665 GPa when no water was involved. Conversely, in region II, effective modulus did not significantly change in response to changes in pulling velocity for both scenarios. We concluded that the viscoelastic behavior observed in region I corresponded to the uncurling of the collagen triple-helix. Water molecules likely play an important role in this viscoelastic behavior.