Abstract: Analysis is done on the composition change of oil fed into the pump of a pipeline. This kind of change causes movement change of crude oil thus making the design value deviate and fluctuate. The fluctuation is unfixed, which is impossible to be forseen. There are many reasons for this sort of fluctuation, which can influence the stability of transportation condition, reduce the efficiency of centrifugal pumps, affect the best quantity of additive and the best oil heating temperature. Therefore the writer points out that it's necessary to control the viscosity of the oil fed into the pumps and its method for either heated or unheated pipeline: To have the on-line viscosity sensor mounted in the sample tube adjacent to the inlet of the pump. It can at any time measure the viscosity of the oil being fed to see whether it is in conformity to the design value. If there is deviation, the actuator can act by means of the regulator to regulate the feeding quantity of the viscosity-reducing agent or the heating temperature so as to maintain the set, viscosity value for stable transportation process, so that viscosity-reducing agent and heating method can be made the best use of to garantee the safety of transportation and reduce the cost.