This paper studied the reaction mechanism and reaction Kinetic in kraft cooking of Xingan Larch. Results indicated that three distict dclignification rate stages occurred during the kraft pulping of Xingan Larch, namely, the initial dclignification stage from the beginning of the cook to 140℃ , 18.82% of lignin was dissolved, the bulk dclignification stage from 140℃ to 170℃ at one hour, 71.35% of lignin was dissolved, the residual dclignification stage from 170℃ at one hour to the end of the cook, 6.51% of lignin was disolved. The activation energy of bulk dclignification stage is 1.33 x 105 J ?mol.