Abstract: 【Objective】To determine ideal ratio of silage corn(SC) and silage pineapple residue(SPR) through in vitro gas generation method, so as to provide guidance for silage corn and silage pineapple residue resource development in southern China.【Method】SC and SPR were mixed in ratios of 100:0, 75:25, 50:50, 25:75, 0:100 and divided into group Ⅰ, Ⅱ, Ⅲ, Ⅳ and Ⅴ. And sample in groups Ⅰ, Ⅱ, Ⅲ, Ⅳ, and Ⅴ were cultured in vitro(3, 12, 24, 48 h). Triplicates were used for each group and 2 blank controls were used for each time point. At the end of each time point, pH, gas production, volatile fatty acids and dry matter degradability(DMD), crude protein degradability(CPD), neutral detergent fiber degradability(NDFD), and calculated the single factor associative effect value of volatile fatty acids, DMD, CPD, NDFD, and multiply factors associative effects index were determined when fermentation ended.【Result】During fermentation, with the passage of time, each pH of each group decreased significantly(P<0.05, the same below);gas production, DMD, CPD, NDFD, total volatile fatty acids (TVFA) increased significantly; concentration of acetic acid(AA) and propionic acid(PA) increased first and then decreased. Early in the fermentation, gas production was low, and the concentrations of TVFA, AA, PA, and butyric acid(BA) increased first before decreasing as the proportion of pineapple residue silage increased. In final part of fermentation, concentrations of TVFA, AA, PA, and BA increased significantly. The single factor associative effect value of CPD and NDFD in group Ⅳ was positive, while the single factor associative effect value of DMD was negative(except for that of 3 h fermentation), and TVFA, AA, PA, and BA(except for that of 48 h fermentation) in group Ⅲ and group Ⅳ were positive. The multiply factor associative effects index of group Ⅲ was the highest at the early stage of fermentations(except for that of 3 h and 12 h fermentation), which 3.83 and 11.85, respectively. The multiply factor associative effects index of group Ⅳ was the highest at the later stage of fermentations(24 h and 48 h), which 20.01 and 21.71, respectively.【Conclusion】The multiple combination impact index is greatest when the ratio of silage corn to silage pineapple residue is 25:75, which promotes rumen microbe proliferation and metabolism and speeds up nutrient decomposition.