The work aims to solve problems such as serious similarity of existing public facilities in old industrial blocks, lack of artistic sense in modeling and failure to highlight the industrial characteristics of the blocks through the research on the improvement design of public facilities in old industrial blocks, to provide new ideas and methods for the protection and renewal of industrial blocks and the inheritance and reference of industrial culture. Existing problems and causes of public facilities were discussed and summarized through field research. According to the existing problems, an improvement design theory model was built, and the improvement design of the public facilities in the old industrial blocks was targeted. The industrial culture was expressed through the design of public facilities to evoke the memory and resonance of culture. The improvement design of public facilities in industrial blocks is based on semiotics. The relationship between symbol "decoding" and symbol "encoding" is deeply discussed, and the model of "decoding-encoding" is established. "Decoding" refers to the analysis of industrial culture symbols and deep meaning. "Coding" refers to the development from four aspects of text image, modeling, function and system, to achieve the final improved design result.