Based on the bi-stable characteristic of quantum cellular automata,the encoder and decoder are designed according to different principles.Simulation is performed using semiclassical simulation method.Compared with the E.N.Ganeshs design of decoder.our design require fewer components and simpler structure.Besides,according modularization design method.we construct II/IV encoder using III/VIII encoder.We also prove that other kinds of encoders with more bits can be built using II/ IV encoder module.Moreover.the method of analysis and design of complex circuit using the principle of the combination of basic circuit module is meaningful for practical work.