Abstract: A Φ500 mm oil pipeline, with 6. 3 km in total length from Qiandian to the 2nd Refinery of Fushun, was put into operation in 1971. The serious wax deposition was found after more than 30 years' operation. According to the theoretical analysis results, the decision to in-line remove wax with 70℃ hot diescl is made. Before the wax removal, a calculation on the length of mixed section and the arrival time of mixed interface are made. A satisfactory wax removal result is obtained in line with the removal program. The maximum throughput of this pipeline is increased from 710-715 m3/h to 770-780 m3/h.