Abstract: Liquid tank is a potential part irradiated by laser in laser-matter interaction research. In this paper, laser irradiation effects on a water tank were investigated by experiments and numerical simulations on the condition that the water was in a natural convection state. The irradiation mechanisms are described as follows: at the initial stage of laser irradiation, the center region of the aluminum wall had an obvious temperature increase due to laser heating, and the temperature of the water near the wall also had a slight increase. With the time evolution, the water temperature became larger and higher, and the magnitude of the max velocity on the line, which was perpendicular to the plate and passed through the laser spot center, kept on increasing in response to the temperature increase, thus the heat transfer intensity continued increasing. With the increase of the heat transfer intensity, the temperature rise rate of the aluminum wall decreased gradually. When the energy absorbed by the wall could be taken away by the water natural convection, the temperature rise rate of the plate center approached zero.