This paper is about a numerical analysis of ablation at the surface of tungsten in high temperature flow. Tungsten has the highest melting point among metals, and it"s hardness and strength properties are outstanding when temperature is high above 2000K. For this reason, tungsten have been used widely in high temperature industries. However when it oxidized, tungsten lost it"s hardness and thermal resistance, and ablation phenomena occurs. To prevent these oxidation and ablation phenomena, we should know about chemical reaction speed of oxidation and probability function about how fast reaction occurs and what species would be produced by oxidation phenomena. In this study, we assumed reaction probability function and made a surface ablation model of tungsten in high temperature. And we performed numerical analysis about surface ablation along time with 2-D axisymmetric cylinder shape. And we compared numerical results with experimental results, and figured out the probability function around 3000K.