With many kinds of initial configurations and spin multiplicities taken in full consideration, the first principile method based on density_functional theory (DFT) has been employed to study the equilibrium geometries, electronic properties and magnetism of BenLa (n=1—18). Our results showed that there are many isomers with extremely close energies near the ground state, thus the cluster is very complex, making the ground state seek quite challenging. The BenLa has magnetism and its stability is far higher than that of Ben+1, indicating that one can acquire magnetic clusters with higher stabilities by choosing the proper doping atom. The Be17La is specially stable and its gap between the highest occupied and the lowest unoccupied molecular orbitals is quite the same as that of the host cluster. The magnetic moment in BenLa cluster system comes mainly from the outer layer unpaired valence electrons and the La element's contribution. The magnetic moment of BenLa is 1μB except that of BeLa and Be3La, which is 3μB.