We have performed an unbiased search for the lowest-energy structures of medium-sized aluminum clusters Aln n=(26~28) using the first principle calculations combined with Wang-Landau algorithm.We focus on the candidate structures from the fragment of the face-centered-cubic (fcc) metal crystal.For the fcc lattice, each atom has 12 nearest-neighbours in the first shell and 6 second-nearest neighbours in the second shell.We distinguish the unequivalent structures by the number of the nearest neighbours and second nearest neighbour, which should be visited in the same probabilities according to the Wang-Landau algorithm.We have got lots of isomers of Aln cluster, which were further optimized by the first principle calculations.It is found that the high symmetry isomer is not the most stable structure for Al(26~28).On the other hand, we have found other more stable structures compared to those previously reported.The lowest-energy structure of Al26 is almost a fragment of the fcc bulk crystal stacked of fcc(111) facets.Next step, we will try to understand why these structures are stable.In addition, we will study the electronic properties of the stable clusters.