Abstract: This paper utilizes element "birth" and "death" finite element technique programmed the subroutine to control the process of filling metal during welding process. Marc, a finite element software, is applied to simulate the three dimensional temperature field of multi-pass welding. Low carbon steel is taken as an example, and welding material filling is conducted step by step during the modeling process. Calculated result of the temperature field is close to experimentaly measured value. Comparing this calculated results with those without considering material filling gradually during multi-pass welding, it is proved that whether considering metal filling step by step greatly influences the multi-pass welding's calculated results, especially when the times of multi-pass welding are excessive it cannot be neglected.