Abstract: The effects of Cu and Zn on spring wheat andactivity of microbes in soil were studied.Tesults showthat aIthough Cu and Zn are necessity for plants ,they will beharmfuI to plants at excess amount.While the concentrationsof Cu and Zn in the soil reached to the toxic level,the yield ofspring wheat would be reduced. However, the contents of Cuand Zn in plant seeds increased. Cu and Zn also inhibited theactivities of microbes in the soil.According to the food hygienestandard ,economic benefit and the normal function of ecosystem,the critical concentrations of Cu and Zn in the studiedsoils were primarily set at 200mg/kg and 350mg/kg.seperately. 

Key words: soil-plant system, copper, zinc, critical content