The one-side V shaped groove fillet welds present asymmetry in the left and right structures, which results in high difference in thermal conduction between the two sides during root welding and affects the quality of post weld forming. In order to obtain these special weld thermoforming laws, a novel equivalent heat source model was introduced in the temperature simulation. The model was based on the Gauss heat source, with consideration to the groove angle effect on the heat source. In order to verify the model accuracy, the temperature field distribution was simulated through the COMSOL multi-physics field software. The differences were compared and analyzed among the common heat source models and the equivalent heat source model for asymmetrical fillet welds. The experimental results confirmed the validity of the proposed model. The thermal cycle curves around the asymmetrical fillet welds were compared and studied. The basis for the heat transfer mechanism of asymmetric fillet welds as well as the variation of penetration forming was revealed. (C) 2018 Published by Elsevier Ltd.