Abstract: The basic principle of drag reduction technology of internal coating and basic method of epoxy coating materials are described.It is pointed out that the key technology of the internal drag reduction is the coating material and coating process.The drag reduction materials at home and abroad, the requirements, coating equipments and coating process of drag reduction materials stated in API Standards are introduced in the paper.The influence of coating adhesion, cleanliness and thickness on the quality of internal drag reduction are analyzed, the defect origins in coating adhesion, cleanliness and thickness are discussed, corresponding measures are investigated and the significance of coating quality control during coating application process is summarized as well.