Optical switch is an important component of integrated optical circuit. In this paper, an on-chip 2×2 directional coupler reconfigurable optical switch based on one kind of chalcogenide phase change materials (Ge₂Sb₂Se₄Te₁) used in the L and C bands was proposed. The switch can be switched by changing the phase state. The optical switching device was designed by means of Mode and FDTD Solutions in the simulation software Lumerical. The results showed that the insertion losses (ILs) were more than -0.36 dB and the crosstalks (CTs) were less than -24 dB in the amorphous state of Ge ₂Sb₂Se₄Te₁ with a coupling length of 24.9 μm in the band from 1500 nm to 1625 nm. The ILs were more than 0.44 dB and the CTs were less than -30.46 dB in the crystalline state. Multi-physics simulation software COMSOL was used to simulate 532 nm wavelength laser heating Ge ₂Sb₂Se₄Te₁. The results showed that a 25 ns short Gaussian pulse with a peak power of 45 mW could transform the material from a crystalline state to an amorphous state. Applying multiple Gaussian pulse arrays with a peak power of 20 mW, a period of 1 μs and a duty cycle of 0.03% could bring it to the crystalline state. Simulation results showed that the designed optical switch can quickly switch optical path in the communication band by laser heating.