Abstract: The purpose of this paper is to study the pressure characteristics and structural deformation mechanism of aluminum honeycomb sandwich plates (AHSPs) under water impact through experimental methods. The self-designed drop test platform was established in the water tank, and the water impact tests on AHSPs were carried out, then the repeatability of the experiment has been verified. On this basis, the water impact load characteristics, deformation mode, permanent deflection characteristics of AHSPs during the process of water entry were studied. Results show that, due to the influence of air cushion effect has a great influence on the pressure, the water impact pressure on the surface of AHSPs is unevenly distributed. Meanwhile, the peak value of water impact pressure at the middle gauging point is larger than that of the 1/4 gauging point, when the drop height is larger than 0.5m. In addition, the elastic-plastic deformation of AHSPs during the water entry process will affect value of the water impact pressure. Namely, compared with the water entry of rigid plate, the peak value of the water impact pressure of AHSPs is smaller. What’s more, compared with the equivalent aluminum plate with the same mass, the value of the peak water impact pressure of AHSPs is smaller, while the pressure duration is longer. For the water impact pressure obtained by different methods in references, the peak values of the water impact pressure approximately increase linearly with the drop height. The deformation modes of the face sheet of AHSPs at different drop heights are almost the same, meanwhile, the rectangular deformation zone composed of four plastic hinge lines is generated in the middle area, and the surrounding area is a trapezoidal deformation zone. What’s more, with the increase of the drop height, the rectangular deformation zone expands around. Besides, with the increase of the drop height, the permanent deflections of front and back faces of AHSPs increase approximately in form of quadratic parabola with decreasing slope. Suffering from water entry impact loadings, the AHSPs will experience large deformation and absorb energy, and the permanent deflections of the back sheet are obviously smaller than those of the equivalent aluminum plate, indicating that the AHSPs have better impact resistance compared with the equivalent aluminum plate.