Abstract: A three dimensional heat transfer model was put forward for the laser-plasma arc hybrid welding, which combines the mathematical models of two heat sources.The model of laser welding is Gaussian volume heat source and its peak heat flux decreases with depth, and the model of plasma arc is Gaussian plane heat source. The influence, induced by reaction between laser beam and plasma arc, was mainly studied in the model.Based on the model, the temperature distribution of 2 mm 1420 Al-Li alloy plate was obtained by FEM computation for laser-plasma arc hybrid welding in different distances of two heat sources.The hybrid welding experiments were conducted and show that the simulation results are well agreed with the experimental results.The result proves that the heat transfer model is more close to physical reality.This paper is instructive to research on heat transfer and process about laser-plasma arc hybrid welding.