Computational fluid dynamics (CFD) study of the blood flow in the coiled cerebral aneurysm is one of powerful tools to explore the treatment mechanism of the endovascular coiling. Although several computational techniques were proposed to represent the realistic coil configuration in the aneurysm for the CFD studies, the CFD methodology for the blood flow analysis in the densely coiled aneurysm is still not fully discussed. The present study develops a CFD approach for the blood flow analysis in the densely coiled cerebral aneurysm without unstructured volume mesh creation. Patient-specific aneurysm geometry with realistic coil configuration was implicitly represented in a Cartesian-grid by using the volume of fraction (VOF) function. A Cartesian-grid CFD simulation was conducted in a finite difference manner with using the VOF function by the method of Weymouth and Yue (J. Compt. Phys., 2011). We conducted that two cases of numerical example of the blood flow analysis in the aneurysm prior to the coiling and after coiling with the packing density of 27%. These examples clearly exhibited that the developed CFD framework successfully resolved the fine flow characteristics around coils in the aneurysm despite the absence of explicit coil surface.