Abstract: Moisture content of the fractured rock mass in the unsaturated zone cannot be measured or calculated up till now, but liquid water in it is very important for ecological regreening and preservation of cultural relics (frescoes). Determination of the ratio of liquid water mass to gaseous water mass (α) is the key to solve this problem. In the open system, which consists of rock mass, gaseous water and liquid water, two-phase water moves and transforms each other continuously, it is in a non-equilibrium state. When the humidity of the system reaches 100%, it is in a local equilibrium state. According to thermodynamic balance principle, density and mass of liquid water and gaseous water are the same in this system, so the ratio of mass of liquid water to gaseous water α is constant. In this paper, the main aim is to find a way to get the value of α. Experiment is designed to record large numbers of data, and to get an empirical formula to get the value of α. The results show that the relationship between α and temperature can be expressed as an exponential function, and the mass of liquid water is much greater than the mass of gaseous water when gaseous water is saturated. The results are very useful to quantify moisture content of rock mass, and helpful in discussion of the transformation law of gaseous water into liquid water each other.