Abstract: According to the sealing performances decreased caused by the sealing clearance of the oil sleeve applied in the drilling rig increased with the temperat ure increased, a study on the thermal expansion law of the oil sleeve was conducted, a calculation formula was derived for the thermal expansion value of the sealing cl earance, the measures to control the thermal expansion of the sealing clearance were discussed and the relative improvements were conducted on the oil sleeve. The e xperiment verification and the theoretical calculation results showed that as the copper wall thickness of the oil sleeve reduced and the steel wall thickness relatively in creased, the improved plan of the steel sleeve material replaced with the 2Cr13 would clearly control the sensitivity of the leakage value to the temperature and would b e favorable to improve the sealing performances.