The work aims to study the effect mechanism of improving tin coating apparent morphology and influencing deposition rate by adding propane sulfonic acid pyridine salt (PPS), imidazole, 3-hexyne-2,5-diol(HD) as representatives of three types of brighteners during the process of electroless tin. The effect of brighteners on the peak potential change of tin deposition in tin plating bath was studied by electrochemical cathode polarization method. The molecular mechanics calculation method was carried out by COMPASS force field in Forcite model to explore the adsorption process of brighteners on the surface of Sn layer and. From the results of cathodic polarization, the addition of brightener could make the peak potential of tin deposition negatively shift. The over-potential caused the horizontal growth rate of nuclei to be greater than that of the vertical growth rate, thus leveling the Sn layer and inhibiting the formation of whiskers to a certain extent. Molecular dynamics calculation results demonstrated that PPS, imidazole and HD had a tendency to be spontaneously adsorbed to the surface of the Sn layer and the adsorption energy of PPS, imidazole and HD in the Sn(111) surface were ?445.338 kcal/mol, ?9.84 kcal/mol and ?22.651 kcal/mol, respectively. The molecules of three brighteners were more likely to be adsorbed on the surface of the Sn layer, thereby inhibiting the growth of the Sn layer to some extent. The adsorption energy of brightener on Sn surface has a positive correlation with the improvement of Sn‘s apparent morphology and reduction of plating rate during electroless plating and provides some theoretical basis for the selection of brightener.