Abstract: Study of vortex shedding character on square cylinder is always hot in the academia. Vortex shedding will appear in the case of fluid flow across square cylinder at a certain flow rate, which may induce cylinder vibration. The impactions of channel width to square cylinders’ vortex shedding characteristic were computed by the code in the case of cylinders with different channel widths. The results show that Strouhal number (St) increases along with channel width; impaction of channel width on fluid’s vortex shedding character becomes stronger gradually; when the ratio of the channel width （H） and barrier size （w） is up to a certain value, slope of line St-B （H/w） will be more gently. It has a tiny contribution to fluid’s vortex shedding character when width of channel increases any longer.