Abstract: In this paper, a discussion on how to determine available roughness value of internal wall has been carried out for the design of gas transmission pipeline.An analysis on the influence of gas transmission pipeline with internal coating to the friction loss, original pressure between stations and the demand horsepower of compressor has been made from the point of view of design and calculation.Taken Zhongxian-Wuhan natural gas pipeline as an example, the paper points out that after the internal coating is applied, the transport capacity of the pipeline can be increased more than 5 %, the outlet pressure of initial station can be decreased to 4.6 %.