Elements Bi and Sb substitute for element Pb in galena. So there must be some defect in the crystal lattice of galena. By means of this crystal-chemical characteristic, it is shown that the Ag-content is not directly proportional to the content of Bi and Sb. Bi和Sb在方铅矿中替代Pb时,方铅矿晶格有缺位,这一晶体化学特征可解释在方铅矿中Ag与Bi、Sb含量间不一定呈正相关。