Using the first-principles calculations within the generalized gradient approximation frame work, we systematically investigate the atomic relaxation, electronic structure, magnetism, and spin-polarization in L21 and B2 structure of Heusler alloy Co2MnAl (100) surface. Due to the difference of Co–Mn and Co–Al bonding, surface atoms in the L21 and B2 structure prefer to move toward and away from the vacuum. By comparison with the bulk, the spin magnetic moments of surface Co and Mn atoms are obviously enhanced due to the surface effects. Our electronic structure calculations show that the gap in L21 structure of bulk Co2MnAl has been destroyed by the surface states and the spin-polarization of CoCo atomic terminated surface in both structures decreases. However, the spin-polarization of MnAl atomic terminated surface is not significantly affected by the surface effects and has a large value in both structures, and this may be the potential in application to magnetic tunneling junctions.