In order to realize the domestic transformation of lubricating oil for a key large imported unit,the replacement scheme and implementation method of lubricating oil were formulated.The replacement lubricating oil was determined firstly through the field investigation,the mixed test of the original lubricating oil and the replacement lubricating oil.Then the detailed oil change scheme was proposed,including the oil change mode and time,oil sample sampling period,etc.Finally,the indexes of the lubricating oil were monitored after the oil replacement of the unit,and the wear condition of the friction pairs of the unit was detected after the operation of 4 000 hours.The oil monitoring results show that the indexes (viscosity,flash point,moisture,alkali value,etc.) and element content of the oil are all in the normal range.The dismantling inspection shows that the wear of the inner cylinder,connecting rod bearing bush and piston is in the normal level,which verifies the feasibility of the lubricating oil replacement scheme.