Abstract: Using the method of Salt gradient Suspension to determine the suspensions ability of pig litter at different fermentation level in the microbial fermentation bed, as well as, based on the appearance of litter, the level degree of fermentation was established. Thirty samples taken from the piggery were classified into four groups. The first group was characterized with shallow degree of litter fermentation, the second group with medium degree, the third group with deep degree, the fourth group with profound. Combining the multiple linear regression, the mathematical equation of the fermentation index of pig litter was established, that was: Y=3.9932-0.0046X1+0.0531X2-0.0484X3-0.0083X4-0.0179 X5-0.0404X6(r=0.9420). The result indicated that the degree of fermentation of unknown litter were judged fast and accurately by utilizing the mathematical equation to determine the fermentation index of unknown pig litter.