With the development of an online power quality monitoring system, the data flagged stipulated by IEC can no longer cope with the adverse impact of voltage variation caused by transient power quality disturbance on flicker detection. This brings great challenges to the technical supervision of flicker source location. Given this, this paper defines the transient voltage variation and gives the characteristic quantity to describe the shape of RMS voltage. Then, based on the IEC flicker meter, it analyzes the influence characteristics and degree of each characteristic quantity variation on flicker detection results, realizes the quantification of flicker level caused by transient voltage variation considering the background, and gives limit value suggestions of amplitude difference. This is verified by an example. Finally, the distribution characteristics of monthly trend data of Plt are summarized based on the data of online monitoring in different scenarios, and a quartile discrimination method using statistical criteria is proposed. The analysis results show the effectiveness of the method. It provides an optional method for rapid screening of monitoring points with flicker exceeding the standard caused by transient voltage variation. This work is supported by the Science and Technology Project of China Southern Power Grid Company Limited (No. 090000KK52190169/SZKJXM2019669).