Abstract: Addressing the problems concerning the manganese series phosphorisation process such as excessive slag formation, uneven color of the phosphorised layer, and the while, gray-striped or yellow phosphorised layer surface, etc., based on the company's years experience in manganese series phosphorisation operation, factors affecting phosphorisation quality are studied and analyzed.As a result, it is identified that the key factors include temperature, time, phosphoric acid proportion, and Fe²⁺ concentration for phosphorisation operation.It is affirmed that the best parameters of manganese series phosphorisation process for oil tubing/casing couples are temperature: ≥ 95℃, total acid point:60, acid proportion:variable as per steel grade(for low grades, 7~8 is the best, and for high grades, over 9 is acceptable), and time:over 20 min.Based on these parameters, the phosphorized film will possesses advantages such as homogeneous distribution, fine crystallization, even thickness, excellent resistances against corrosion, wearing and bonding.