Abstract: The hot water preheating method has ever been used for commissioning of country-cross pipelines carrying viscous crude oil. The use of this method will bring about the problems, if applied in the eastern China with adequate water sources, such as lengthening the time of commission, vying for water with agriculture, pollution of enviroment and dear cost, and, if used in northwest in China where it is short of water and unconvinient to deliver diesel oil, the problems will be getting even more serious. All this makes the author to conceive the idea as to putting into direct com-mission by applying a certain quantity of mobility improver in crude oil which is able to reduce the pour point and viscosity. Also touched in the article are the industrial application of viscosity reducing technology, the effect shown in the experiments that has made three times in industrial pipelines, and some key problems while using it for direct commission such as selection of mobility improvers, the conflict between the pressure permisable on the part of a pipeline and the flow rate of the oil commissioned, the essential points of operation at commission. Comparison between the two methods is made.