During the Steam Generator Tube Rupture (SGTR) accident in Lead-cooled Fast Reactors (LFR), the high-pressure subcooled water is continuously injected into the liquid metal, causing the flashing and endothermic vaporization. The processes can degrade core heat transfer performance and directly threaten the safe operation of the reactor. Studying the thermal hydraulic activities from liquid metals to water are significant in advanced nuclear energy technology. An experimental platform for injecting high-pressure subcooled water into high-temperature medium is established. Thermal oil is used to simulate the injection process of the SGTR accident. The effects of test section gas space, injection time and thermal oil temperature on pressure impulse and temperature disturbance are experimentally studied. The pressure impulse, pressure rising rate and maximum peak pressure are higher under the small gas space conditions by comparing the pressure variations of two typical gas spaces. The subcooled water produces bubbles due to the combined effects of depressurization-induced flashing and heating-induced vaporization when the thermal oil temperature exceeds the saturation temperature of water, and the process facilitates the accumulation of pressure impulses. Additionally, long injection times can enhance temperature disturbances in the oil pool. The results offer a theoretical foundation for developing interphase heat transfer and volume expansion models of the liquid metal-water interactions.