Bed expansion behavior and sensitivity analysis for super-high-rate anaerobic bioreactor (SAB) were performed based on bed expansion ratio (E), maximum bed sludge content (V(pmax)), and maximum bed contact time between sludge and liquid (tau(max)). Bed expansion behavior models were established under bed unfluidization, fluidization, and transportation states. Under unfluidization state, E was 0, V(pmax) was 4 867 ml, and tau(max) was 844-3 800 s. Under fluidization state, E, V(pmax), and tau(max) were 5.28%-255.69%, 1 368-4 559 ml, and 104-732 s, respectively. Under transportation state, washout of granular sludge occurred and destabilized the SAB. During stable running of SAB under fluidization state, E correlated positively with superficial gas and liquid velocities (u(g) and u(l)), while V(pmax) and tau(max) correlated negatively. For E and V(pmax), the sensitivities of u(g) and u(l) were close to each other, while for tau(max), the sensitivity of u(l) was greater than that of u(g). The prediction from these models was a close match to the experimental data.