To evaluate the effects of severe side reactions on the product yield of pyrolysis of coal tar with iron oxide oxygen carriers (OCs), simulation experiments were carried out and analyzed by thermogravimetry mass spectrometry. The reactions occurred between iron-based OCs with different reduction states and carbon black (CB) and syngas products. The H-2 present in syngas showed the lowest initial reaction temperature and the highest decrease in concentration, indicating its strong reactivity. Because CO reacted with iron-based OCs at a higher temperature and had a slow reaction rate, the relative reactivity at the low temperature stage is lower compared to H-2. At the high-temperature stage, the reaction of CO was inhibited by CH4 and the concentration of CO was affected by the reactions of CB. CH4 had the highest initial reaction temperature and least consumption but a higher reaction rate than CO in its narrow temperature range. Therefore, CH4 clearly affected the side reactions at high temperatures. Scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis of the solid residues shows that the consumption of CB is low and the Fe/O ratio in the solid residues is larger, owing to the higher relative reactivity of syngas with different reduction states of iron-based OCs.