Abstract: As the natural heat convection of the oil in pipelines and the heat changes a long the leaglli of pipelines are negligible, the heat transfer of the crude oil in pipelines is a two-dimensional unstable heat conduction. Based on similitude principle, the author gives the criteria oorrclatioas between oil temperature and the physical guantiry of such affected factors as t₀、t_∞、α、U、λ、a、r etc, after shut-down. Backed up by the actual cases of Bhut-ciown, he makcs out a set of temperature reduclion law dicgrams for engineering application.