This paper investigates impact loads on the legs of a jack-up rig during the stand-on/off-bottom procedure. The magnitude of the impact loads is theoretically estimated by introducing a simplified simulation derived from the energy concept, which means the decrement of kinematic energy of the rig during bottom contact is considered to be the absorbed energy by soil. The equivalent linearization method is applied in frequency domain analysis to solve the equations of rig's motion with/without bottom contact. The calculation results are compared with the experimental ones to show the validity of present new approach. It is found that present study will be of suitable help to improve conventional design criteria.