Abstract: On the basis of the dominant physical processes of secondary electron emission, the relationship among secondary electron yield, the ratio of the mean secondary electron generation of one backscattered electron to that one of a primary electron, primary energy, the parameter E(z), maximum yield and backscattered electron coefficient was deduced. From the experimental results, the formula for the ratio in the energy range of 2 to 10 keV was given. Based on the relationship deduced, the parameters E(z) related to six metals were computed with experimental results, respectively. The parameter E(z) related to six metals is found to be approximately 11.89(eV)0.5. Based on the deduced relationship and the computed parameter, a universal formula for expressing the secondary electron yield as a function of maximum yield, backscattered electron coefficient and the primary energy was deduced. The secondary electron yield calculated from this universal formula and the yields measured experimentally from metals were compared. Therefore, the formula presented is universal for secondary electron yields from metals in the energy range of 2 to 10 keV.