Based on the characteristics of the technology and heat source of double-sided laser beam welding for T-joint,a new heat source consisting of a Gauss surface heat source and a self-adaptive body heat source is presented. The Gauss surface heat source represents the action of the heating effect of plasma cloud above the keyhole surface,and the self-adaptive body heat source represents the action of the Fresnel absorption and inverse bremsstrahlung absorption of the laser energy in the keyhole,and the effects of keyhole on the heat and mass transfer are also considered. Using the FLUENT software,a three-dimensional mathematical model for double-sided laser beam welding for T-joint is established,and the characteristics of the temperature field and keyhole are analyzed. The result shows that the molten pool temperature and keyhole shape distribute symmetrically along the stringer center. The molten pool temperature gradient on the cross section increases as the distance from the center of stinger center increases,especially on the skin side,and the maximum length of molten pool locates the keyhole interacting position rather than molten pool surface,the primary reason is the heat source coupling action of both sides. The simulated results agree well with the experimental results,which proves the accuracy and applicability of the model.