The positions of the impurity ions of Nd3 ,Th4 ,Sb5 in PbWO4(PWO) crystal are simulated by computer technology.The corresponding defect clusters energy is calculated.The defect chemistry and the formation of the defect clusters are discussed.The mechanism of the doping effects of Nd3 ,Th4 ,Sb5 are studied.The calculation results show that the Nd3 and Th4 would occupy the Pb sites near V2-Pb,and restrict the 420 nm absorption band by compensating the electronegative charges of V2-Pb.When the PWO is doped with high concentration,the Sb5 would occupy the W sites near V2 O,make the V2-Pb capture two holes more easily to form the colour center of 420 nm absorption.The conclusions are detailedly discussed.