On the basis of the electromagnetically induced transparency (EIT) phenomenon which occurs in three-level Λ-type coherent media modulated by rectangular barriers, a theoretical scheme is proposed to achieve an all-optical switch at a weak light level. The Maxwell-Bloch equations are derived to describe the dynamic evolution of optical pulses in the system under the semi-classical framework. By the multi-scale method, the nonlinear Schr?dinger equation (NLSE) describing the propagation of optical pulses under the modulation of rectangular barriers is obtained. In different incident cases, such as single optical soliton incidence, as well as symmetric and asymmetric double optical soliton incidence, this study systematically investigates the excitation properties of propagation modes and cut-off modes in the rectangular barrier. Moreover, it analyzes the influence of the phase of incident double optical solitons and the intensity and width of rectangular barriers on the propagation properties of different modes in rectangular barriers. Finally, this paper proposes an all-optical switch at a weak light level by changing the characteristic parameters of rectangular barriers and the phase of the incident optical pulses.