The present work was addressed to understand the contributions of the heat-treatment temperature and inorganic catalysis to the combustion characteristics of biochar. A cornstalk sample was leached by water and HCl to partially and fully remove active inorganic elements, respectively. The raw and leached samples were heat-treated at the temperatures of 200-900 degrees C. The resulting biochars were subjected to X-ray diffractometry and Raman spectroscopy analyses for structural characterization and thermogravimetric analysis for combustion characteristics, particularly, for char reactivity. It was found that the heat-treatment temperature has a significant effect on the evolution of the biochar structure, while inorganic matter has little influence. For low-temperature (200-400 degrees C) biochars, the heat-treatment temperature has a considerable influence on the devolatilizaiton and a marginal effect on char combustion behaviors, while the inorganic species, particularly, water-soluble species, have considerable influence on the behaviors of both stages. For high-temperature (500-900 degrees C) biochars, the heat-treatment temperature and inorganic matter are both important to char reactivity. The high contents of inorganic species of cornstalk resulted in the catalytic effect of inorganic species dominating over the influence of the carbonaceous structure ordering on char reactivity. With active inorganic species removed by leaching, char reactivity of biochars turned to decreasing monotonically with an increase of the treatment temperature.