The invention provides a determination method for flue gas emission impunity periods of a coal-fired power generator unit. The determination method comprises the following steps that a starting period of the power generator unit is calibrated; a shutdown period of the power generator unit is calibrated; low-load operation time points of the power generator unit are calibrated; data missing time points caused by CEMS faults and other irresistible objective reasons are calibrated. The determination method can achieve the effect of determining the over-standard periods of pollutant concentration under special circumstances, and the timeliness and the accuracy of environmental protection electricity price calculation of flue gas emission of the coal-fired power generator unit are achieved.