Abstract: By means of operation data obtained from pigged hot oil pipeline and the viscosity-temperature law of waxy crude oil discovered from laboratory, the methodology for determining on-line viscosity-temperature relationship for piped.hot waxy crude oil is established, and with the method, the actual viscosity-temperature relationship on actual pipeline is given.The paper points out that the viscosity-temperature relationship obtained from operation data of piped hot waxy crude oil after pigging is more closer to the property of actual fluid of pipeline compared with that of laboratory.