Abstract: The influence of the thermal insulation layer with thickness changed from 0 mm to 72 mm on measuring response of grease stain thickness in oil pipeline using the fast neutron transmission method and scattering method was reported. The experimental device consists of the transmitter of neutron beam, detector of neutron and the BH1224 computer multi-channel analyzer. The experiment results show that the sensitivity of detection of pipeline grease stain falls with the increase of the thermal insulation layer, but the influence is smaller on transmission method than scattering method. The neutron counting number is suitable for linear fitting with semi-logarithmic on neutron transmission method and with quadratic polynomial on scattering method. The average of R² is 0.995 8 and 0.997 9, respectively.