Abstract: There are many changes in the soil microbial biologic content during the application of fertilizer in the surface of black soil for a long time．The results show that the assorted usage of nitrogen，phosphate and potassium fertilizer can keep the MBC of fallow arriving to 1．6g／kg；the assorted usage of high amount of organic and inorganic fertilizer can increase 1．96～ 2．75 times than that of fallow;a 1ong time of ertilization and cultivation results in the microbia1 biologic content(MBC)attenuation；in al1 treatments，the percent of MBC increases from bigger to smaller，being M₂+NPK (+ 141．25％ ，begin in 1990)>M₄+NPK(+126．88％)>M₂+NPK(+ 101．25％ ，begin in 1980)> M₄+ CK(+80．63％)>1．5(M₁+NPK)(+13．13％)>NPK(+8．12％)，the percent of MBC decreases from smaller to bigger，being M₀+NPK(-3 75％)>M₁+NPK(-17．50％)>M₂+CK(-30．63％)>CK(-47．50％)>M₀+CK(-61．88％)．