The coral-inhabiting snail Coralliophila violacea is a common species in the Indo-Pacific coral reefs and it usually lives on the surface of its host, Porites spp. In this study, field survey on the distribution of C. violacea on poritid corals, Porites spp. among sites were conducted. And the influence of flow rate on the distribution of snails was also examined through a simulation model. The sampling sites were northeastern of Taiwan, Taitung, Penghu, Lutao, Hsiao-liu-chiu and Lanyu. The presence of spatial variability in the relative abundance of C. violacea on porited corals has been observed. The highest percentage of corals with snails was in northeastern Taiwan, i.e. 45% and the lowest ones were in Lutao and Lanyu, i.e. 12%. The distribution of snails among sites were heterogeneous (X2-test of independence; p<0.001). Significant differences of shell length in snails among sites were also found. Among them, the distribution pattern of shell length in snails from Lutao and Lanyu was not normal. Difference in the age-distribution of snails among sites was present. In general, five and six years old snails were most abundant. A lack of snails under two years old had been found in Lutao, Lanyu and Penghu. Based on the simulated downward trajectory of snail larvae, it was indicated that a minimum substratum for larval settlement varied with flow rates and depth of water.