A method of operating liquid in a vacuum or low-pressure environment and observing the operation and a device for the operation and the observation respectively, including the steps of preparing a housing, putting the housing in the vacuum or low-pressure environment and control liquid, vapor, and buffer chambers under the same temperature, infusing vapor into the vapor chamber through a gas inlet and control the vapor pressure inside the vapor chamber to be equal to the saturated vapor pressure of a liquid specimen inside the liquid chamber under the same temperature to prevent the inside liquid from volatilization, and evacuating the buffer chamber through the pumping port to pump out the vapor and prevent the vapor from exhausting through outer apertures out of the housing. A probing source can pass through the outer, inner, and vapor apertures for observation and analysis of the liquid specimen inside the liquid chamber.