The generalized gradient approximation (GGA) based on density functional theory(DFT) is used to analyze the structural and electronic properties of the unclassical endohedral fullerene M@C22(M=Sc, Ti, V, Cr, Mn, Fe, Co and Ni). It is found that the ground-state structure of the unclassical fullerene C22 is a spin singlet cage containing one four-membered ring and the doping of transition metal atom can obviously enhance the stability. It is discovered that the C-M bond have both the covalent and the ionic characteristics. The analyses of magnetism, energy levels, orbital wave functions and density of states show the hybridization between the 3d orbital ofM atom and the C atomic orbital in C22. In addition, Ti, Cr, Fe and Ni atoms become non-magnetic after they have been doped into the C22.