Abstract: The thermal model and mathematical model for a heat, power and gas cogeneration system were established.The models were used to calculate the changes of gross coal consumption and energy availability coefficient of a heat, power and gas cogeneration system with two types of coal when gas output was 10000 m³·h^-1, boiler steam load was 130 t·h^-1.The minimum gross coal consumption and the maximum energy availability coefficient were found from the calculation results.The energy availaility coefficient μ could be used as a criterion for evaluating the multi-production system.