Lateral overflow integrated capacitor (LOFIC) technology is an important method to improve the dynamic range of complementary metal-oxide semiconductor (CMOS) image sensors. However, the charge overflow mechanism in LOFIC pixels has not been thoroughly studied. An analytical model is proposed for the charge overflow process in LOFIC pixels. The electric field superposition principle is used to analyze the potential barrier along the charge overflow path. The regulation mechanism of the transfer gate voltage and light intensity on the charge overflow process is studied by iterative simulation method. The results show that the full well capacity of the pinned photodiode can be increased by reducing the transfer gate voltage and increasing the light intensity. In addition, the charge accumulation rate and charge overflow rate increase with increased illumination but are not affected by the transfer gate voltage. The model is verified with technology computer-aided design (TCAD) simulations and experimentally tested on a 100 nm-thick chip fabricated via CMOS process. The simulation and measurement results exhibit good consistency with the proposed model.