Abstract: The principle, experiment and conclusion on the grease stain measuremeng using fast neutron are reported. The experiment equipments consist of Am-Be fast neutron source, ZnSdetectou and BH1224 multichannel spectrometer. Paraffin is used instead of real grease stain. Steel plates are used in stead of pipeline. The results of the experiment indicate that there is a good linearship between the logarithm of the reciprocal of the neutron transmissivity and the paraffin thickness. The measuring accuracy of the paraffin thickness is 0.6 mm in this experiment.