Catalytic depolymerization of kraft lignin was successfully carried out in isopropanol/water mixture system over Rh/La2O3/CeO2-ZrO2 catalyst at 373 degrees C for 2 h with Fe as reductant. The selectivity of in-situ H-2 was increasing from 67 wt% to 98 wt% by changing the proportion of isopropanol and water with metal Fe. A one-to-one correspondence was established between liquid products distribution and H-2. It was an efficient method for predicting the composition of the liquid oil by H-2 selectivity detection or converting kraft lignin to desirable liquid products optionally, which administered to reduce the dependence on the specific catalysts. Other temperatures and catalysts were a viable option for the relationship.