Abstract: During pipeline transportation, depressant-treated crude oil is inevitably influenced by the shear action from pumps and pipes. Studies show that both pump and pipe shear actions have influence on the low temperature flowability of crude oil in the temperature range where exists the peak zone of wax precipitation, and that the shear action of pipe flow exceeds that of pump in the cause of gradual temperature drop. It is proved from the research point of view that shear action varies with oil composition and pipeline length. Being subject greatly to shear action, the effectiveness of depressant must be evaluated on the basis of the simulation on pipeline transportation.