Optofluidic is a technology that adjusts the optical properties of the system by manipulating microfluid. Microfluidic optical switch plays an important role in integrating multiple components into a unitary microfluidic chip and implementing a reconfigurable microfluidic optical path. In this paper, a pneumatically 2×2 optical switch with the reconfigurable optical path is designed. By compressing the gas to control the states of an adjustable air gap mirror, the optical switch function is realized by making light transmission and total reflection alternately in the microfluidic channel. Simulation results obtained with COMSOL software show that the extinction ratio is 10.2dB and the switch period can reach up to 60ms. It is demonstrated that this switch has good performance, and can be integrated with other models to manufacture complex microfluidic devices for various functions.