Abstract: The research on characteristics of oil film pressure was usually conducted based on the assumption of fluid incompressibility neglecting the impact of compressibility and the journal inertial force on oil film pressu re.Oil film pressure however,will dramatically change with the varying time when subjected to transient shock heavy load,while density and viscosity of oil film are the function of oil pressure,thus the incompressibili ty assumption is no longer applicable in this case.Besides,the acceleration caused by shock loading exists in the journal and the inertial force of journal due to high motion of the journal cannot be neglected as well. Both the compressibility and the inertial force of journal were introduced in the calculation of oil film pressure to work out a result well agreed with practical one.