As a novel biomass gasification technology, chemical looping gasification (CLG) could in situ catalytically crack biomass tar by oxygen carrier (OC). This study compares the reactivity of different OCs (Al 2 O 3 , Fe 2 O 3 , NiO, NiO+Fe 2 O 3 , and NiFe 2 O 4 ) to crack a biomass tar model compound (toluene) and preliminarily explores the reaction mechanisms of toluene cracked by NiFe 2 O 4 OC. Among five OCs, NiFe 2 O 4 with a homogeneous Fe/Ni dispersibility shows the best reactivity for toluene cracking with a toluene conversion and H 2 yield of 96.83% and 0.91 L/g, respectively. Additionally, on the basis of the dispersibility of active sites on the OC sample surface, the reactivity of the other four OCs to crack toluene shows the sequence NiO+Fe 2 O 3 > Fe 2 O 3 > NiO ≫ Al 2 O 3 . A large amount of carbon deposition, including amorphous carbon and graphitized carbon, is generated during toluene catalytic cracking, while the addition of steam significantly eliminates the carbon deposition. The NiFe 2 O 4 OC shows a dual-function of in situ oxidation−catalysis during toluene cracking. A mechanism of four steps is proposed for the toluene cracking on OCs: (I) toluene cracking at high temperature, (II) reduction of OC, (III) generation of amorphous carbon deposition and (III′) formation of graphitized carbon, and (IV) elimination of carbon deposition.