Abstract: A pure-Lagrangian vortex method, based on Instantaneous Vorticity Conserved Boundary Conditions (IVCBC), is adopted to build the numerical calculation model of flow around double circular cylinders that have the same structure characteristics of two side by side circular cylinders. The Wide Wake (WW)and Narrow Wake(NW) appear in the range of pitch ratio T/D=1.1~2.6. A scheme is proposed to distinguish the NW and WW through the direction synchronism between induced velocity at the middle of double circular cylinders and deflection of gap flow. By comparing the directions of the above two flowing conditions and analyzing the classic case, it is concluded that the proposed method could distinguish WW and NW accurately, which offers an important numerical calculation method for investigating the flow characteristics in this range.