Abstract: Abstract：Nanomaterials have been concerned many attentions, researchers use Lead sulfide quantum dots in all sorts of fields due to the special optical property. In our study, in order to explore the performance of the Lead sulfide quantum dots, we adopted chemical process to control the size of the sample. Lead sulfide quantum dots were prepared by Liquid phase method and morphology features of the sample was tested by XRD and TEM, the optical property was tested by UV-vis. The size of the particles is changed under the condition of controlling the concentration of the reaction solution and the addition of the surfactant and the particle size of the nanoparticles varies between 7 and 20 nm, which results in the change of the optical properties and the band gap of the particles. The optical band gap of lead sulfide QDs increases drastically with the decrease of the diameter of the sample QDs. Due to the test result, the sample with high crystallinity was successfully prepared by chemical process, and the test result shows the rule of quantum dot size change. By the research of the optical property, Lead sulfide quantum dots can get a better achievement in the solar cell and enhance the improvement of the novel materials. Key words: Lead sulfide; quantum dots; Band gap; Modulation