Abstract: The study on the broad-beam influence of the grease stain thick response using the amplitude spectrum of the transmitted γ- ray is reported. The simulated experimental device consists of a collimating beam of 137Cs γ- ray, a NaI(Tl) scintillation detector and a BH1224 multi-channel spectrometer. The experiment results indicate that there is a linear relation between the response and the grease stain thickness. When the measuring grease stain thickness response, the slope of the calibration line is negative with the photoelectric peck spectrum zone; with the Compton spectrum zone as a result of broad-bean, the slope is positive, but its slope value is rapidly reduced when the pipeline diameter is increased; with the total spectrum zone, its slope is positive for the thin pipeline, but its slope is negative for the wide pipeline. The error between the measured correction factor β to 1 is all less than 2%.