Abstract: DV-Xα molecular orbital method was employed to study the electronic structure of perovskite La1-xCaxMnO3 cubic system where the dopant concentrations are different. The dependence of magnetic and electrical properties on the dopant calcium concentration have been investigated. It was found that the spin-dependent Mn3d-O2p hybridization occurs in the whole perovskite La1-xCaxMnO3 system. The conductivity of the undoped system is metallic and the DOS (density of state) at Fermi level in major bands is higher than that in minor bands. With the increase in dopant concentration x, the conductivity of the manganite changes from metallic to half-metallic and the magnetic moment of Mn decreases monotonously in conformity with the changing regularity of the exchange splitting of Mn3d bands. The doped Ca increases the overlap of Mn3d and O2p orbits to intensify the Mn-O-Mn superexchange and cause the magnetic ordering of CaMnO3 to present G-type antiferromagnetism. Meanwhile, LaMnO3 presents orderly ferromagnetism due to the weak overlap of Mn3d and O2p.