It has been confirmed that iron oxides can catalyze the Fenton reaction and promote the Maillard reaction. However, there is still no consensus on whether they can play a facilitating role during the decomposition of straw. In this study, four dosages of goethite (0%, 0.5%, 1% and 5%) were added into wheat straw for 60 days of aerobic composting to investigate whether it can promote decomposition and the optimum added dosage during composting. And the water-extractable organic matter (WEOM) is considered as an indicator of organic matter conversion and can be monitored by UV-Vis and three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy to evaluate the maturity of composting. The results showed that the influences on straw decomposition and humic substances formation were obviously different with various added dosage of goethite. 0.5% goethite addition had the highest decomposition rate (23.8%) and significantly higher than the control (22.4%), while the decomposition rate of 1% and 5% goethite addition were significantly lower than the control, 20.6% and 19.5%, respectively. In addition, the increase in UV-Vis spectral parameters, including the specific UV absorbance at 254 nm (SUVA₂₅₄) and at 280 nm (SUVA₂₈₀) were facilitated by goethite addition. And the humic-like substances region (including fulvic acid-like and humic acid-like substances) of fluorescence regional integration (FRI-EEM) increased by the order of 0.5% dosage (47.0%) >1% dosage (45.3%) >0% dosage (45.2%) >5% dosage (43.6%) after 60 days of composting, indicating that the appropriate addition of goethite remarkably improved the transition of organic matter and accelerated the maturity process. Therefore, goethite can be a suitable additive to improve the quality of end products for straw composting, and the best treatment in this study was 0.5% added treatment based on dry weight. The results will provide a theoretical basis for the research and application of new straw decomposition promoters by using iron oxides.