In order to expand the applicable band range of the encoder, a multi-band Terahertz wave 4 ×2 encoder based ontwo-dimensional photonic crystals is designed. The performance of the encoder is thoroughly studied and analyzed using Rsoftsoftware combined with the plane wave expansion（PWE） method and the finite-difference time-domain（FDTD） method. The research results indicate that the output transmittance of the encoder varies with the lateral offset of the dielectric pillars at thewaveguide branch. After optimizing the design of the Terahertz wave 4×2 encoder, it can achieve high-contrast 4×2 encoding logic functions in the wavelength ranges of 103.80 ~108.57 μm, 109.19~111.12 μm, and 111.94~114.08 μm, with a contrast ratio ofno less than 9.30 dB and a maximum of 29.47 dB, and a response time is not more than 16.04 ps.