Abstract: The deployment of gas compressor stations and units is the most difficult part of the project design. The backup mode of compressor unit is one of the important determinants. In China, however, the choice of backup mode is often described qualitatively, without intensive study on various kinds of backup modes. Firstly, the analytical method of process system is adopted to intensively review the backup modes of compressor unit. The advantages and disadvantages, essential difference and suitable conditions of such backup modes are sorted out and compared. Finally, the methods to select backup mode of compressor unit for long-distance gas pipelines are defined. In other words, the backup mode of compressor unit should be selected by both considering the characteristics of the pipeline system and comparing the technical and economic indicators in its full life cycle.