Oxygen-steam gasification of biomass catalyzed by modified iron-rich red mud extract is firstly performed in our work. During the impregnation of the modified red mud extract (MRME), the pore structure characteristics and thermal behavior of the maize straw changed significantly. The influence of MRME on syngas quality, gas yield, and thermal efficiency were performed in a lab-scale gasification reactor. The results showed that higher temperature, sufficient MRME addition, appropriate equivalent ratio (ER) and a small amount of steam all promoted syngas quality and energy conversion. For maximum economic efficiency, the optimal rate of MRME addition is 30% weight ratio to maize straw. The optimal level of ER was found to be 0.23, and the maximum energy conversion ratio was 82.4% at 800 °C with optimal levels of MRME addition and ER. Compared with the raw maize straw gasification at the same operating condition, the content of H2 increased from 17.32% to 33.77%, and CO raised from 22.89% to 35.11%. It seems that the red mud extract catalyst has the potential for using as an economic efficiency industrially catalyst for high quality and H2-riched syngas production from biomass gasification.