In this experiment, the fermented pineapple residue (FPR) was replaced with 0% (CON), 25% (T25) and 50% (T50) in the diet based on silage royal grass roxb for 30 days in the fattened fatten bulls to evaluate the effect of FPR on growth performance, serum indicators and rumen characteristics.Thirty Simmental calves were selected and divided into three groups according to a completely random design.The temperature and humidity of the cowshed shall be measured every day.Rectal temperature and blood of cattle were measured, and blood and immune markers were measured.The results showed that the rectal temperature decreased significantly when adding 25% fermented pineapple residue (P<0.05), and the rectal temperature decreased significantly when adding 50% fermented pineapple residue (P<0.01).The content of T4 and TC in serum of cattle in T50 group was significantly lower than that in the control group (P<0.01), and the content of T3 was significantly higher than that in the control group (P<0.05), and the content of CR was significantly lower than that in the control group (P<0.01). Fermented pineapple residue can indeed improve the oxidative (heat) stress resistance of finishing cattle. In the correlation experiment, bacterial genera such as Succinniclassicum, Melainabacteria, Lachnospiraceae, and Fibrobacteres all showed significant or extremely significant correlations with heat stress-related indicators.