The invention relates to a voltage flicker measurement method for a power quality measurement instrument. According to acquired voltage effective value envelope data and a preset identification function, sliding convolution calculation is carried out to obtain an identification value. When positive and negative changes happen to the identification value, extreme values in a corresponding convolution calculation section and time corresponding to the extreme values are searched and acquired. According to a difference value of each two adjacent extreme values and the time corresponding to the extreme values, a flicker value in a measurement time period is calculated and obtained. The calculation method completely meets a definition that voltage of a power system is influenced by large load random switching by flicker according to a national standard, the method can be used for flicker calculation with periodic changes or random changes, and the measurement accuracy is high.