Abstract: Working principle of the localization system for pipeline robot is analyzed in this paper.Electromagnetic field distribution of the ultra-long wave emitter is studied and a parameterized mathematic model is established.Symmetrically distributed antenna array is adopted as the signal receiving equipment for ultra-long wave.Both nonlinear and linear localization algorithms are presented to realize spatial localization of the pipeline robot crawling in unknown underground or underwater pipelines.Industrial field tests verify that both the localization system and the algorithms are efficient,and with the plane localization precision less than 15 cm,they are able to meet the demands of engineering tasks such as pipeline operation and inspection.