In order to investigate the effect of transplanting density and biochar application on soil physical and chemical properties and rice yield，a two-year experiment was carried out containing an interactive test of two levels of planting density(12.85×104，18.36×104 holes/hm²)and four levels of biochar application rate(0，10，20，30 t/hm²)，with Liaogeng 401(Oryza Sativa，japonica rice)as the tested rice variety.The pH，Eh，CEC，BD，DOC and N2O emissions of paddy fields were studied to investigate the effects of transplanting density and biochar application on efficiency of fertilizer.The SPAD value，dry weight and yield composition factors and actual yields of rice were studied to investigate the effects of transplanting density and biochar application on the growth and yield of rice.The results showed that:On the condition of the same amount of biochar application，the transplanting density increase had no significant influence on the pH，Eh，CEC，BD and DOC of paddy soil，reduced the N2O emissions without significant difference among the treatments，and increased the dry weight and yield of rice.On the condition of the same transplanting density，the biochar application increase had no significant influence on the Eh，CEC and BD，increased the pH and DOC significantly，reduced the N2O emissions and the dry weight of single plant，and increased dry weight，productive panicle numbers and grain yields of rice. The yield of rice of M1B30 and M2B30 treatments significantly enhanced by 5.7% and 5.2%，respectively，compared to those of M1B0 and M2B0.The results indicated that the transplanting density of rice was the main factor affecting rice grain yield，and the application of biochar enhanced the fertilizer use efficiency by improving soil physical and chemical properties；Increasing the amount of carbon application under high transplanting density can significant increase rice yield ；by comprehensive consideration，maximum rice grain yield can be obtained with the planting density of 18.36×104 holes/hm² and the biochar application of 30 t/hm² in this research.