Many traditional Chinese medicine (TCM) decoctions are proven to have multiple functions in animal production. These decoctions are seldom recognized by the international scientific community because the mechanisms of action are not clearly elucidated. According to TCM theory, Cortex Phellodendri (COP), Rhizoma Atractylodes (RA), Agastache Rugosa (AR), and Gypsum Fibrosum (GF) can be used to formulate a medicinal compound that prevents or cures animal disease caused by heat stress. The aim of this research was to study the regulatory functions of the active components of TCM and to elucidate the effects of different TCM decoctions on antioxidant activity and lipid peroxide content, using in vitro and in vivo models of heat stress. For in vitro experiments, intestinal crypt-like epithelial cell line-6 (IEC-6) cells were employed to evaluate the effects of the active components of COP, RA, AR, and GF. For in vivo experiments, forty-eight 2-mo-old Chinese experimental mini-pigs (7.20 ± 0.02 kg) were randomly assigned to 4 groups: a normal-temperature group (NTG); a high-temperature group (HTG); HTG treated with COP, RA, AR, and GF (1:1:1:1, TCM1); and HTG treated with COP, RA, AR, and GF (1:1:1:0.5, TCM2). Results showed that the active components of the COP, RA, AR, and GF increased (P < 0.05) the proliferation and viability of heat-stressed IEC-6 cells and that the most effective treatment doses of COP alkaloid, RA Aetherolea, Herba Agastachis Aetherolea, and GF water extract were 200, 100, 100, and 200 µg/mL, respectively. All 4 active components increased (P < 0.05) superoxide dismutase, glutathione peroxidase activities, and glutathione content, and decreased (P < 0.05) malondialdehyde content with respect to the heat-stressed group to concentrations similar to those seen in NTG. In vivo experiments demonstrated that TCM1 and TCM2 improved (P < 0.05) the poor growth performance seen in HTG pigs. The superoxide dismutase, glutathione peroxidase activities, and malondialdehyde content in porcine jejunum treated with TCM1 and TCM2 were not different (P > 0.05) from those seen in the NTG and were better (P < 0.05) than results seen in the HTG. Overall, it appeared that TCM2 was more effective than TCM1 in ameliorating the effects of heat stress in pigs. In conclusion, this study revealed that the active components of common TCM decoctions have antioxidant functions.