Abstract: The bubble penetration depth in coolant impacts the safety operation of lead-based cooling reactor after steam generator tube rupture (SGTR). In order to study the SGTR accident for China lead-based reactor, the penetration depth characteristics of bubble jet into lead alloy were simulated by water experiment, the penetration behavior was observed by the high-speed photography technology, and the whole process evolution of bubble flow pattern was achieved. The experimental data of bubble flow pattern and penetration depth were obtained, and the relationship between the bubble dimensionless penetration depth and Froude number was derived. The relationship can also predict well in the case of smaller density ratio of the bubble jet into the liquid metal coolant based on Froude similarity criterion. The experimental results show that the bubble penetration depth is proportional to the steam initial speed under certain condition of the break area. The relationship of bubble penetration depth obtained by dimensional analysis has a good agreement with literature result.