Experimental results are presented on the gasification of pine sawdust pellets using high temperature steam as the gasification agent. Downdraft gasifier was adopted as reactor, the reactor temperature was varied from 700℃ to 950℃, and steam to biomass ratio (S/B) was changed from 0.3 to 1.0. Based on biomass gasification technology, the gasification characteristics of pine sawdust pellets were deeply discussed. In addition, numerical computation using Gibbs free energy minimization was applied and compared with the experimental results. The results show that hydrogenrich gas could be effectively produced by high temperature steam in downdraft gasifier, and the carbon layer played an important role in preparation of hydrogenrich gas, in which steam reforming reaction and tar cracking were taken place. H2 and CO yields would rise at higher temperature, and H2 volume fraction would reach the peak when reactor temperature raised some value，H2 fraction would decline if the temperature was continued to raise. The increase of S/B could develop H2 content of product gas, temperature of material bed would be dropped by some endothermic reactions, and the increase of H2 volume fraction was restrained. In the test, the peak value of H2 volume fraction was 47.67% with S/B of 1.0 and temperature of 900℃. These results also provide the operating law for downdraft gasifier with high temperature steam.