Higher butanol/acetone ratio is always desirable in ABE fermentation, and this ratio is closely associated with the complicated patterns of metabolic reactions and NADH generation rate. The patterns of acetate/butyrate formation and re-assimilation in multiple closed reaction loops, as well as NADH regeneration in ABE fermentation using different substrates varies. In this study, we evaluated butanol/acetone ratio in ABE fermentations utilizing cassava and corn based media by graph theory and NADH regeneration analysis. The theoretical calculations and experimental data revealed that a lower metabolic strength in butyrate loop and enhanced NADH generation rate were responsible for the achievement of higher butanol/acetone ratio when fermenting cassava based substrate. In traditional fermentations and extractive fermentations with oleyl alcohol/bio-diesel as the extractants when using cassava based substrate, butanol/acetone ratios reached 2.24, 2.84, and 2.19 with the increasing increments of 14.9, 61.4, and 6.8% respectively, while butanol productivities stayed at comparably high levels as compared with those of the fermentations when cultivating on corn based substrate.