Based on the features of LD end-pumped Yb3+:Y2 SiO5 laser crystal and considering the convective heat transfer on the side faces, the temperature distribution, pumped-face distortion and thermal focal length under different pump power were obtained by solving anisotropy heat conductive equation through finite difference method. The thermal focal lengths before and after considering the heat-transfer coefficients were calculated respectively. And the thermal focal length was further measured experimentally. The experiment results demonstrate that the tendency of thermal focal length changing with pump power agrees well with the theoretical result.