Abstract: Polygeneration technology makes more reasonable use of energy to enable sustainable energy utilization. As opposed to separate chemical engineering and power generation systems, a polygeneration system demands more specific performance on the gasifier. The equilibrium working temperature of the gasifier and the composition of outlet syngas at this temperature were calculated by solving chemical equilibrium and energy equilibrium equations. The analysis was used to study the effect of gasifying agent mixing ratio on outlet syngas composition,cold gas efficiency, thermal efficiency and exergy efficiency. The optimum O₂ coal ratio was found for a reasonable steam coal ratio(steam coal ratio had little effect on efficiency) for various kinds of coal to maximize thermal efficiency and exergy efficiency. These results can be used as a reference for optimization of polygeneration systems.