The invention relates to a power grid frequency measuring circuit capable of eliminating the flickering and inter-harmonic interference. The measuring circuit comprises a voltage conversion unit, a reference source unit, an active filter unit, a comparison circuit unit and a data calculation unit. The voltage conversion unit is connected with the active filter unit, and the active filter unit is connected with the comparison circuit unit. The comparison circuit unit is connected with the data calculation unit. The reference source unit is respectively connected with the active filter unit andthe comparison circuit unit. According to the invention, the frequency information on the two sides of the power frequency in the power grid is filtered through the hardware filtering mode. After that, a stable analog signal is obtained, and the frequency value of the power grid is obtained through average calculation. The calculation amount of a CPU can be greatly reduced, and the inter-harmonicand flickering influence can be effectively eliminated.