The invention relates to the field of thermal control, and discloses a measurement method and device of fly ash carbon contents. The method can comprise the following steps of: carrying out phase space reconstruction on the historical value of an auxiliary variable corresponding to the historical data value of the fly ash carbon contents to determine a phase point corresponding to the auxiliary variable; receiving the current value of the auxiliary variable; and according to the historical data value of the fly ash carbon contents, the phase point corresponding to the auxiliary variable, the current value of the auxiliary variable and a prediction model for the fly ash carbon contents, calculating the current value of the fly ash carbon contents. The method is simple and easy in operation, a complex device is not required, and the safety and the economy of unit operation can be improved.