In order to understand the flat compressive properties of the thermoplastic honeycomb panel, the flat compressive strength formula was obtained by analyzing the flat compressive deformation mechanism of the thermoplastic honeycomb panel, and then the influences of structural parameters and ambient temperature on the flat compressive strength of the honeycomb panel were analyzed. The experimental results are in agreement with the theoretical analysis. With the increases in cellular core aperture ratio, side length and height, the flat compression strength decreases. The flat compressive strength increases with the increase of honeycomb core panel thickness.