Welding process is expanding to various fields because of its rapidity and accuracy. And, precision of shape of the workpiece of this is needed more than before. It is difficult to predict shape of workpiece because welding process includes multi physics including flow of pool and thermal dynamics. Moreover this process needs high energy as heat input, so real-time observation is difficult because of generating a high temperature and luminance in welding process. In this present, we show usability to compare cross-section of workpiece between computational simulation and experiment in laser welding.