Abstract: Relative study displays that during flowing of crude oil in pipes, not all the wax precipitated would deposit on the pipe wall due to the washout function of oil flow, therefore, the flowing behavior and wax precipitation law of crude oil are analyzed to present a method to calculate the effective wax precipitation.Laboratory experimental results for 9 kinds of crude oils show that the wax deposition rates fast lower down with the effective decrease of wax precipitation when it is slight, while wax deposition rates decrease accompanying by a slow deposition velocity when the wax precipitation increases effectively to a certain extent.