Abstract: The motion of binary tropical cyclones is numerically simulated using a nondivergent, barotropic model with no basic flow. The interaction of binary tropical cyclones is investigated applying the asymmetric theory. Each of binary tropical cyclones will mainly be displaced by the asymmetric flow passing its centre(i.e. the ventilation flow). This asymmetric flow is induced by the superposition of the asymmetric gyrescreated by the linear and nonlinear effects itself and the asymmetric vortex formed by its counterpart tropical cyclone.