Abstract: The mechanism of tritium-labelling by Wilzbach method has been investigated using CNDO/2 method. The results show that in the case of radiation-induced labelling,the species such as HeT+,T2+,T+,T3+,participate in the tritiation of harringtonine, but in the case of labelling by electric discharge, the species are electron, tritium atom, and other reactive species. The calculated results agree with experimental values. It seems that calculation of the superdeloca-lizability Sr (E) , Sr(N), and Sr(R) using CNDO/2 method may be used as a useful tool for the location of tritium labelling on Chinese medicinal herbs.