By using the Linear Muffin-Tin Orbital (LMTO) method and synchrotron radiation photoemission,the electronic structure and surface stability of ZnSe(100) nonreconstruction surface,c(2×2) undimerized and c(2×2) dimerized reconstruction surfaces have been theoretically and- experimentally investigated.We find that ZnSe(100)c(2×2) undimerized surfaces is more stable than ZnSe(100) nonreconstruction surface and c(2×2) dimerized reconstruction surfaces, supporting the experimental results proposed by Farrell.Through discussing surface states,we have found the- difference between ZnSe(100) reconstruction surface and c(2×2) undimerized surface. The theoretical result is in good agreement with the synchrotron radiation photoemission measurements.