The present paper deals with the fertility ehange of black soil after its cultivation from the virgin land in Heilongjiang province.Results obtained showed that under the influence of mechanical cultivation and current agricultural system,signifieant changes on the properties of black soil were brought by its cultivation.The development of soil fertility has been found in three stages—aetlvation,cultivation and restoratlon.It was observed tliat with the Increase of the time of cultivation,the thiekness of humus horizon,the oontente of humus,total N,hydrolyzed N and the value of C/N were decreased;at the same time, the soil aggregates were disintegrated gradually,the amount of soil microaggregate and its G₁-fraction,and the humus carbon and total N in both G₁ and G₂ fraction of microaggregate were depressed;the specific gravity and volume weight of soil were inoreased,whereas its porosity was deereased.The amount of available P and K inereased in varying extent following the developing of eultivation of the soil. The crop yield was higher in the first ten years after reclamation, and then a significant depression was found.