In the Intense 14 MeV Neutron Source Facility OKTAVIAN of Osaka University, Japan, which produces fusion neutrons by D-T reaction, we have many experience in handling tritium targets and tritiated contaminants. In OKTAVIAN, the transition of tritium concentration in urine and exhaled water of some workers was measured with a liquid scintillation counter for years. Using the measured results between the concentration of tritium in urine and in exhaled water, we have found a simple method to lead excretion parameters in order to estimate the internal exposure dose. The first decreasing term, HTO component, was expressed as a simple exponential function with the measured concentration of HTO in exhaled water. The second and third decreasing terms, OBT component, were expressed as a sum of two exponential functions using the difference between the concentration of HTO in exhaled water and the total tritium concentration in urine in equilibrium. And the excretion function of total tritium in urine can be expressed as a sum of their three exponential decreasing terms. Moreover, without measurements of longer-term, it becomes possible to analyze the longer half-life in OBT component at a short time.