A method for on-line soft measurement of coal-fired carbon oxidation factor of power generation boiler include such steps as selecting key variables, coal property parameter and boiler/unit property parameters as input vectors of soft measurement model, selecting them as input vectors, selecting them as input vectors, and selecting them as input vectors of soft measurement model. At the same time,the parameters of ash and fly ash after coal combustion are measured, and the carbon oxidation factor is calculated as the output vector of the soft sensor model. An on-line soft-sensing model of carbon oxidation factor was established, After establishing the soft-sensing model of coal-fired carbon oxidation factor of power generation boiler, if on-line measurement of coal-fired carbon oxidationfactor under a certain operating condition is required, only the measurement data of the following variables are assigned to the input vector X, and the calculated y is the carbon oxidation factor OFdifferent kinds of coal under different boiler loads. The invention modifies the carbon oxidation factor issued by the Intergovernmental Panel on Climate Change, so that the result is closer to the actual value. It can realize on-line measurement, real-time monitoring and boiler carbon combustion control of coal-fired boilers.