Abstract: In order to prevent oil leak of the linear reciprocating shaft in soft packer, following the analysis of the movement of the linear shaft and the reasons of oil leakage, a new oil sealing device was designed.An air ring isolation was formed in the sealing ring at the end of shaft, by introducing compressed air into the annular space between the shaft and sealing ring, the positive air pressure forced the excess oil on the shaft surface back into the inner cavity, and at the same time cooled down the shaft.A comparative test was conducted between YB25 and YB28 soft packers, the results showed that after six months running, the sealing device without air ring for the linear shaft in YB25 needed to be repaired; while that with air ring in YB28 still ran properly, no oil leak was found, the longer working life of sealing device could save 3 459.78 RMB yuan each half year.This method provides a technical support for promoting the efficiency of packing machine.