The invention belongs to the technical field of ferrous metallurgy and relates to a method for measuring an interface heat transfer coefficient under a pressurization condition. The method comprises steps as follows: two through holes and two blind holes are drilled in a casting mold and are perpendicular to the side wall of the casting mold; a double-platinum-rhodium thermocouple externally connected with wires is inserted in each of the four holes and is fixed by intertwining corundum bi-pass pipes and asbestos strings, and thermocouple welding temperature measurement points are exposed; molten steel is injected into the casting mold, and data measured by the thermocouples are input into a computer through a temperature data acquisition instrument in the solidification process of the molten steel; source codes for calculation of the following interface heat transfer coefficient is written in Fortran language in combination with Beck nonlinear estimation; the source codes are verified through ProCast. The method for measuring the interface heat transfer coefficient under the pressurization condition can be used for a high-temperature and high-pressure pressurized steelmaking process in a poor temperature measurement environment and is simple, convenient, reliable, safe and accurate.