Abstract: The effects of penetrating agent on the properties of eucalyptus woodchips chemi-mechanical pulping were studied. The results showed that the performances of different type of penetrants were quite different in the eucalyptus woodchips chemi-mechanical pulping properties. Among these, sodium diethylhexyl sulfosuccinate penetrant exhibited the best performance on improving the impregnation of eucalyptus woodchips. With the dosage of penetrant of 0.4%, the chemical liquor absorption amount and NaOH absorption rate of wood chips respectively increased by 7.34% and 9.97% respectively, if they were compared with the blank groups. At the Canadian standard freeness (CSF) level of 300 mL, with the addition of 0.4% sodium diethylhexyl sulfosuccinate at the impregnation stage, the refining energy consumption and shives content in pulp were reduced by over 9% and 46%, respectively, if they were compared to the control pulp sample. And the tensile strength, burst strength and tear strength were increased by 11.4%, 14.3% and 15.6%, respectively, without losing brightness.