La2O3 doped SiO2B2O3Nb2O5 (SBN) complex phase glassceramics were prepared by controlled crystallization method. The effects of La2O3 doping on structure and energy storage performance of SBN complex phase glassceramics were characterized by DSC, Raman, XRD, SEM, ferroelectric and dielectric tests. The results show that La2O3 doping can effectively improve the thermal stability of complex phase glassceramics. With the increase of La2O3 content, the crystallization barrier of the system increases, the thermal expansion coefficient decreases first and then increases，the valence bond vibration intensifies, the dielectric constant increases first and then decreases, and the dielectric loss decreases first and then increases. When doped with 1.00% (mole fraction) La2O3, the energy storage density and energy storage efficiency of complex phase glassceramics under 40 kV/cm are the highest, which are 0.031 J·cm-3 and 77.6%, respectively. The energy storage performance is mainly evaluated by the synergistic effect of dielectric constant and breakdown field strength. La2O3 can improve the dielectric constant by improving structure stability and reducing dielectric loss. When La2O3 is introduced into the system, it is in the voids of glass network, which can effectively enhance the breakdown resistance of material. The complex phase glassceramic structure can increase structural disorder, thereby reducing relaxation loss and effectively improving the energy storage performance of material.