Photosynthesis is one of the most sensitive processes to lead, but the effects of lead on the transformation of light energy of plants are still not clearly understood. In the present paper, spinach was cultivated in the experimental fields and was sprayed with various concentrations of PbCl2 solution. We investigated the effects of lead on the activities of photochemical reaction and the key enzymes of carbon assimilation in spinach chloroplast. The results showed that Pb2+ treatment could significantly inhibit the Hill reaction activity of spinach chloroplast and photophosphorylation, and it had a more conspicuous effect on cyclic photophosphorylation than non-cyclic photophosphorylation. The activities of ATPase on the thylakoid membrane were severely inhibited under Pb2+-treated condition, and Ca2+ ATPase activity was affected more obviously than Mg2+ ATPase activity. Meanwhile, the activities of the key enzymes of carbon assimilation were also significantly reduced by Pb2+, especially Rubisco activase. The reduction of dry weight of spinach caused by Pb2+ was more significant than that of fresh weight. It implied that Pb2+ could disturb light energy transformation of chloroplast.