Kuchino-erabu volcano recently erupted in August 3, 2014 and May 29, 2015, which are considered that the plume discharged from the vent did not form dense pyloclastic flows but dilute pyloclastic surges. Pyloclastic surges travel down slopes in very high speed with very high heat that may cause serious damages to human property and life. In order to manage and mitigate the risks of pyloclastic surges, it is severely required to predict traveling range of pyloclastic surges. In this paper, the authors present analytical model of pyloclastic surge, considering the phenomena as a kind of gravity-driven density currents flowing downward on inclined slopes. The model is applied to the eruptions mentioned above and compared with the actual range of pyloclastic surges. Also the rheology of pyloclastic surge is mentioned counting the computational results.