Abstract: The experiment compared soil nutrients,pyrolytic and infrared ray spectra characteristics of humic acid of soil between un-cropped and cropped lands to determine the effects of cropland ecosystems on gray desert soil nutrients and humic acid characteristics.The results show increase in soil organic matter,total N,total P,total K,slowly-available K and available N;but decrease in available P and available K,while there is a slight decrease in soil pH after planting.The fatty lateral chain of humic acid in un-cropped land soil is much more than that in cropped land soil.The fat characteristics of the humic acid in un-cropped soil is stronger than that in cropped land soil.Soil humic acid is older under cropland ecosystem conditions.