A two dimensional numerical study is carried out for flow past five inline square cylinders of similar size ‘D’ at Re = 150 for studding flow behavior. The gap spacing (g) between the cylinders is varied from g = 0.25–5. The flow structure mechanism is analyzed in terms of vorticity contour visualization, time-history analysis of drag and lift coefficients and physical parameters. Under the effect of gap spacing, four distinct flow modes are identified. These are, i). Shear layer reattachment flow mode, ii). Semi-developed irregular vortex shedding flow mode, iii). Fully-developed two rows vortex shedding flow mode and iv). Two rows single bluff body flow mode for cylinders C1-C5. In Force Statistics, the values of Cdmean, Cdrms, Clrms and St are calculated. The mean drag coefficient represents mixed trend by increasing the values of gap spacing for cylinders C3, C4 and C5. The maximum value of Cdmean is found at g = 5 for cylinder C1, that is 1.4594, while the minimum value of Cdmean is for cylinder C3 at g = 0.25. There may also observed some negative values of Cdmean for cylinder C2 at g = 0.25–2.25 and for cylinder C3 at g = 0.25–1.25 due to effect of thrust. Furthermore, St shows increasing behavior at small and large gap spacing i.e = 0.25–0.75 and = 1.5-5. While decreasing behavior at moderate gap spacing. The greatest value of Strouhal number is examined at g = 5 for cylinder C5, i.e 0.1521.