The feasibility of deuterium mass transport prediction from falling droplets of Pb-17Li was verified. This prediction is one of key techniques of the engineering design of tritium extraction device for the fusion reactor. The mass-transfer-coefficient, deduced on the surface-stretch-model was applied. As the experimental results, deuterium mass transport in the falling droplets from four different size nozzles, at four temperature conditions between 375 °C and 450 °C, performed by the authors, were compared. Resultant Sherwood number was between 494 and 598, and explained the experimental result of the two orders of magnitudes differences with the reported diffusion in static condition. Though, the ratio of theory and experiment still remained between 1.8 and 2.3. Simple boundary condition, not considering the number of oscillation, wide range of reported diffusivity value are considered to be main reasons of the deviation. The analysis model including these factors is to improve prediction accuracy. This result is expected to contribute to a preliminary design of a tritium extraction device.