Based on the optical phase change material Ge₂Sb₂Se₄Te₁ and the optical waveguide structure, a reconfigurable 2×4 mode multiplexing optical switch device is proposed to improve the optical communication capacity. The device is composed of two 1×2 multiplexing switch units with a slanted waveguide structure and a 2×2 multiplexing switch unit with symmetrical structure. First, the mode transmission characteristics in the waveguide are analyzed by the mode coupling theory. Second, the optical switching device is modeled by the three-dimensional finite difference time domain method. Finally, the model is used for experimental research. The research results show that when the working wavelength is 1550 nm, the insertion loss of the 1×2 switch unit when the phase change material is in the crystalline state and the amorphous state is as low as 0.60 dB and 0.06 dB, and the extinction ratio is as high as 19.55 dB and 27.58 dB, respectively. The minimum insertion loss of the 2×4 mode multiplex switch in the entire C-band (1530--1565 nm) is 0.23 dB, and the maximum extinction ratio is 19.12 dB.