Circulating tumor cells in the patient's body are present at less than 1000cells / ml. Since it is very small compared to blood cells, it is necessary pre-enrichment process which removes the erythrocytes in blood. To enhance the CTCS enrichment process, microchannel was designed as a arrow feather. Also, the inertial force is applied only at high flow rates within the microchannel. This Inertial force differently acts on cells according to the size difference of cells. After confirming the pre-test using 13 μm, 6 μm and 2 μm particles, MCF-7 and red blood cells be used for cell separation according to size. As a result, we acquired cell separation efficiency which applied CTCs and red boold cells.