Recently, demand for the fan-out wafer level package is increasing because the market of IoT（Internet of Things）devices is expanding. Especially, higher accuracy and higher productivity are required for the chip-on-wafer bonding process. However, the process has the issue about the recognition accuracy caused by heat haze on the heated wafer. Therefore, the authors examined the quantification of thermal fluctuation behavior which fluctuates due to the temperature of wafer and jet flow by the thermo-fluid analysis. The bonder units such as bonding head, wafer and camera were modeled to clarify the thermal fluctuation behavior in the die bonder. The influence of the heated wafer and jet flow on the velocity and temperature of air was evaluated by the thermo-fluid analysis. Furthermore, the validity of the analysis was verified by the particle image velocimetry（PIV）.