In order to explore the depolymerization characteristics of alkali lignin in the hydrothermal system with formate and Pd /C,seven kinds of formates were selected to conduct experiments.The results show that optimal conditions are a nickel formate and Pd /C amount ( with respect to raw material) of 10%,a reaction time of 30min and a reaction temperature of 325℃,and under such conditions,the liquid product yield in depolymerization products is 56.24% and the overall yield of four monophenols is 12.14%,By comparing high resolution mass spectra,organic elements and thermogravimetric characteristics of the control sample with those of the sample with nickel formate and Pd /C,it is found that the addition of nickel formate and Pd /C is helpful in the deoxygenation process of hydrothermal reaction of lignin,and causes more products of smaller relative molecular mass to produce.