Abstract: Thermal effect of heat source and fluid flow in weld pool for laser full penetration welding titanium alloy were investigated. The results show that the laser fully penetrated weld shaping of titanium alloy depends on the thermal effect of "two points and one line" heat sources and the fluid flow in weld pool that is influenced intensively by heat input and laser power density in welding. With increase of heat input and laser power density, the thermal effect of metal plasma and metal vapor as well as the fluid flow and the heat transfer in weld pool increase obviously, and the cross section of weld transforms from nail shape to near X shape. A model for the temperature distribution, which includes two point heat sources that lie on the top and bottom surface of the workpiece respectively amt one line heat source, is proposed.