Abstract: Pigging technology plays an important role in cleaning, inspection, maintenance and operation of pipelines in oil and gas industry. Because of the variety of kinds of pig, knowing about the functions and principles of them will be useful for the rational picking and application. In this paper, the pigs with different functions are introduced. The cleaning pigs are divided into mechanic scraping type, jet washing type and gel cleaning type as their different principles. Isolating pigs are divided into polyurethane type, ball type, gel type as their materials; detection pigs can be sorted by their functions, including inspection of geometric configuration, geographic information, metal loss, leak testing, etc.. Maintenance type pigs are divided into coating pig and plugging pig. Based on the advantages and disadvantages of different pigs, the paper also reveals their problems in abrasion, sealing, blocking, etc. The development trend of pigging technology in the future is looked ahead.