This system is a system for analyzing blood flow which imposes a boundary condition relating to the blood flow to three dimensional shape data of a target vascular site of a subject and divides a lumen of the target vascular site into meshes for obtaining state quantities of the blood flow at each mesh position by means of computation, having: a labeling unit, by a computer, for reading out the three dimensional shape data on the lumen of the target vascular site, and labeling a plurality of vascular elements included in the target vascular based on a size of the cross-sectional area of each of the vascular elements; wherein, the computation of the state quantities is carried out by varying a level of mesh detail for each vascular element based on the labeling according to the size of the cross-sectional area.