In this study, carbon and nitrogen stable isotope analysis was used on collagen extracted from an unclearly classified pig bone sample from the Pingfengshan shell midden site in Xiapu County. The δ¹³C value of this sample was determined as -12.2‰, and the δ¹⁵N value 4.9‰. The value of carbon isotope ratio indicates that the food consumed by the pig contained both C₃ and C₄ plants, but mainly C₄ plants. The nitrogen isotope ratio shows that the pig was less carnivorous and of a lower trophic level. However, the value of δ¹⁵N is still higher than the contrast group of wild boars and wild terrestrial mammals. Based on comprehensive study, it is argued that the feeding of the pig depended on human supply to some extent, thus the pig was likely to have been cultivated. Meanwhile, the C₄ plant sources in the pig’s food structure suggest that millet farming may have existed at the site.