Results of field experiment applying sweet clovers, wheat straw anti heat in black soil showed that there were significant differences among the ratcs of decompositiun of the oganic materials. The decomposition rate of sweet clover was greater than these of the other two organic materials, and that of peat was the lowcet either in tlic black soil of Harbin or in that of Keshan. The humification coefficient of peat in the soil was the highest, that of wheat straw the second, and that of sweet clover the lowest. Experimental results also showed that application of the organic materials incremnd the contents of humus and nutrients, improved the retention oblity of the soil fo.r nutrient.s, and increased the total C and additional complexing degree of organo-complexes in soil. It was also found that the content of loosely cambineci humus was increased, that of closely-combined humus was decreased, and the humus was activated by application of onganic meterials, and the colloidal characteristics and the fertility art the black soil were improved.