The enhancement of the bioavailability and process controllability of trace elements (TEs) addition is of significance to improve the anaerobic digestion (AD) performance. In order to understand the bioavailability of TEs, the chemical form distribution patterns of endogenous/exogenous Fe, Ni and Co with different dosage ( Fe: 1, 10 and 100 mg/kg; Ni and Co: 0.1, 1 and 10 mg/kg) and different pH condition (6.5; 7.5 and 8.5) were investigated in three different anaerobic digestates. The results showed that the exogenous TEs dosage exerted no obvious effects on the TEs distribution patterns. The chemical fractionation of TEs was more affected by pH, redox potential, AD process and digestate resource. Under pH 6.5 and with redox potential rising, the acidextractable and reducible fractions and of Fe, Ni and Co were increased while the oxidizable fractions were decreased, which enhanced the bioavailability of TEs.