Abstract: While adding derpressant in the crude oil to be transported through pipeline and heating the oil up to a certain temperature can reduce oil's pour point and viscosity and thus improve its low temperature rheo-logical properties, adding drag reducer can moldify flow pattern, reduce friction loss and realize the purposes of energy saving and consumption reduction. The comprehensive treatment technology for depressant addition has been successfully applied in low flow pipelines, and considerable benefits have been achieved. However, application of depressant in fully-loaded pipeline came across several technical problems due to the big flow, high flow rate, small inter-station heat loss, station desigh of thermal load insufficient for secondary heat, treatment, as well as the pump station not having extra pressure. Field tests made in Qin -Jing Oil Pipeline show that applying depressant in fully loaded pipeline is quite promising, and that combination of depressant with drag reducer, which deteriorates low - temperature rheological properties, has a limited application future.