In order to effectively cope with the feed safety risk caused by illegal additions, improve the detection methods of feeding fat and oils and meet the supervision requirements of feed quality and safety, reliable animal fat and oils were collected, and experimental sample set was obtained by adulterating different proportion (1%, 5%, 10%, 20%, 30% and 40% W/W) of ruminant fats in terrestrial animal fat and oils. Fourier transform infrared spectroscopy (FTIR) combined with stoichiometric analysis was used for discriminant analysis of ruminant constituent in terrestrial fat and oils. Results showed, for the sample set of 1%～40% adulteration proportion, the correct discriminant rate of partial least squares discriminant analysis model was 100%, and no false positive and false negative was found. For the sample set of 0.1%～40%, 0.2%～40%, 0.4%～40%, 0.6%～40% and 0.8%～40% adulteration proportion, the correct discriminant rates were all lower than 100%. With the decrease of the lowest adulteration proportion, the number of false positive and false negative obviously increase, the correct discriminant rate decreases gradually, and the detection limit of FTIR discriminant analysis is proved to be about 1%. The discriminant analysis mechanism was further discussed by comparative analysis of fatty acids, infrared spectral band and chemical bond. It was proved that the absorption peaks at 3 006 cm-1 (representing the tensile vibration of C—H (cis-)) and 914 cm-1 (representing the flexural vibration of HCCH(cis-)) of non-ruminant samples were higher than those of ruminant samples. These mainly reflected the significant difference of cis and unsaturated fatty acids. The absorption peaks at 965 cm-1 (representing the flexural vibration of HCCH(trans-)) of non-ruminant samples were lower than those of ruminant samples, reflecting the significant difference of trans and saturated fatty acids. The content of trans-CC bond for 1% adulteration proportion was significantly higher than the other samples of lower proportions. There was no significant difference for the content of cis-CC bond and C—H (—CH2—) bond between the samples with different adulteration proportions. Therefore, the discrimination of ruminant constituent in terrestrial animal fat and oils by FTIR was mainly based on the characterization of trans-CC bond structure. In summary, infrared spectroscopy can be used as a technique to discriminant ruminant constituent in terrestrial fat and oils with both high efficiency and accuracy.