Two kinds of humic acids derived from different coal sources have been studied for three years. The results show that it is feasible to use humic acids as urease inhibitors. They could slowly reduce the decomposition of urea, lessen nitrogen pollution of environment, and significantly improve the activity of crop roots and the available utilization rate of soil nutrients. Also humic acids could be got easily and have little harmful effect on environment and organisms. While exploiting weathered coal resource,it could improve environmental conditions.