Li2MnSiO4 is one of the potential cathode materials for lithium batteries due to its high capacities, but the poor conductivity hinders its further development. The cycling performance and electrochemical property of Li2MnSiO4 cathode material can be improved by doping metal cation. Twelve structures LixMn1-yMySiO4 (x=2, 1, 0; y=0.5, 1; M= Al, Fe, Mg) by doping Al, Fe and Mg are constructed in this paper, and their structures, electronic properties and delithiation process are studied by using the density functional theory of first principles within the GGA+U scheme. The best doping site and delithiated structure are found by comparing their energies. The results show that Al-doping is the best way to improve the conductivity and cyclability of the cathode material Li2MnSiO4. The pure Li2MnSiO4 has a low conductivity because of its large band gap (3.41 eV), while Al-doping Li2MnSiO4 crystal has metallic characteristics due to its electron densities of state with up-spin and down-spin cross through the Fermi level. The band gap is also reduced when it is Fe-doped, which improves the conductivity of Li2MnSiO4. Among the delithiated structures LixMnSiO4 (x=1, 0), Al-doping enhances the structural stability because of the lowest formation energy and its cyclability is improved by reducing the volume change. Within the lithium ion extraction from the Li2MnSiO4 and Li2Mn0.5M0.5SiO4 (M=Al, Fe, Mg), the Mn-O and M-O bonding have much more ionic features, while the covalent bonding feature between Si and O is almost unchanged. And the fully delithiated MnSiO4 and Mn0.5M0.5SiO4 show semic-metallic properties depending on the density of states of configuration. The delithiated voltages for the first Li extraction process decrease when Al and Fe are doped. Therefore the Al-doping in the Li2MnSiO4 is expected to be an effective way to improve the cycling performance and electrochemical property for Li-ion battery cathode material.