The toxicity of yellow-brown earth added with Cu, Cd, or Pb was researched using the MICROTOX method in the process of successively growing of paddy and wheat in a pot experinvent. It was confirmed that when three metal elements in yellowbrown earth were extracted by water, their concentrations were too low to display toxicity as contrasted with red soil; but when extracted by 0.1 mol L^-1 HCl, their concentrations rose obviously and toxicity appeared. The optimum quasi-conjunction equarion between metal's concentration in soil and its remanent luminosty (toxicity index) was founded on the basis of correlation significance at p=0.01 level. The critical remanent luminosity of soils containing metals was defind as 90% (EC₁₀). Accordingly, the critical concentrations of Pb, Cu and Cd in yellowbrown earth (grown with preceeding crop) were estimated to be 488-587, 17.8-25.3 and 1.11-2.12 mg/Kg soil, respectively.