This paper studies the average-irradiance dependence in the frequency response of the three-phase correlation image sensor (3PCIS). For the ac component of the photocurrent, a small-signal equivalent circuit of the 3PCIS pixel is derived. Based on this circuit, it is found that, for each fixed modulation frequency, the transfer function of the ac photocurrent from the photodiode to the NMOS multiplier transistors is formulated as a negative-phase high-pass filter in terms of the dc photocurrent, which is proportional to the average irradiance. A method is then proposed that compensates the irradiance-dependent frequency response by inverse filtering pixel by pixel. In experiments, the irradiance dependence in the frequency response of a 64×64-pixel 3PCIS chip is measured and analyzed to estimate a key parameter. By using the estimated parameter, the output images of the 3PCIS are successfully compensated for the irradiance-dependent frequency response, with the phase error being less than 1° up to 5 kHz modulation.