The lattice parameters,band structures,density of states,electron density differences and optical properties of La,Ce,Nd doped SnO2 are studied by density functional theory (DFT).The computational results show that the bond length near La are greatest changed,while the change near Nd are least,which indicates the lattice distortion caused by rare earth doped in SnO2 is related to the covalent radius of doping atom.The band structure shows that rare earth doping can make the band gap of SnO2 narrow.The La doping makes the band gap reduced 0.892 eV comparing that of intrinsic SnO2,and Nd doping induces three energy levels in the forbidden band.The electron density difference shows that rare earth doping makes the electron redistribution of SnO2 and the iconicity enhance,especially the existence of f electrons.La atom loses electrons most and Nd atom loses least,which are consistent with the calculated results of band gaps.The calculated results of optical properties show that the imaginary part of the dielectric function and absorption function have a red shift,which agrees well with the calculated results of energy band gap.