Abstract: Wax deposition is a severe flow assurance challenge for waxy crude oil transportation. Generally, mechanical pipeline pigging is used to remove the wax deposits on pipeline wall. However, the field pigging operation relies greatly on the experience due to the poor understanding of wax removal mechanism, and pig plugging and wax blockage occur frequently. Here, the fundamental issues in wax removal by pigging of crude oil pipeline were summarized, the research progress from the perspectives of wax removal mechanism, wax removal efficiency and wax breaking force was clarified, and it was also pointed out that the mechanical strength of wax deposits, rheological properties and flowing characteristics of the oil-wax slurry in front of the pig, as well as the critical condition for wax plug formation, would be key issues and main directions of future research in this field.