Abstract: The incubation experiment and pot experiment were conducted to study the effects of different C/N combinations of fertilizers(corn straw+urea)on biological fixation and release of nitrogen fertilizer and wheat growth.The results show that the biological nitrogen fixation is improved with the increase of C/N ratio.But the releasing rate of microbial biomass nitrogen decreases gradually.With the increase of C/N ratio of fertilizer combination,the restraint to nitrate nitrogen in soil becomes stronger.When corn straw is applied to wheat field,the C/N≤20 is suitable for the growth of wheat.