The invention discloses an automatic quantified water injection method for high-temperature hot water. The method includes: to-be-heated water is injected into an inner container, a first pressure induction control switch is turned off, a second pressure induction control switch is turned on, a power supply is turned on to heat the inner container so as to heat the water, the inner container transmits heat energy to a high pressure generating device, the high pressure generating device generates large pressure and transmits the large pressure to the second pressure induction control switch to turn off the second pressure induction control switch, and the inner cavity of the inner container is isolated from external atmosphere; a heating mandrel continues heating the inner container, pressure of the inner cavity of the inner container increases to open a fluid pressure valve, and liquid flows into a communication mechanism through the fluid pressure valve and flows towards a water injection mechanism through the communication mechanism; the water injection mechanism closes automatically, the heating mandrel continues heating the inner container, the inner pressure of the inner container increases, the high-pressure liquid is conveyed from a first guide pipe to the first pressure induction control switch to turn on the first pressure induction control switch, the inner cavity of the inner container is communicated with the external atmosphere, and the inner pressure of the inner container recovers to normal pressure.