Abstract: To address this gap, a two-dimensional fully kinetic model is developed by coupling the Particle-In-Cell (PIC) method with a Monte Carlo Collision (MCC) scheme, incorporating photon-induced detachment reactions to simulate the photo-neutralization of high-energy negative ion beams. The model self-consistently solves the Poisson equation and particle equations of motion while accounting for photon collisions and neutral-particle interactions, enabling a detailed description of the spatiotemporal evolution of ions, electrons, and neutrals in a laser neutralizer. Preliminary comparisons with available experimental data validate the reliability of the model. Systematic simulations further reveal the effects of laser intensity, wavelength, and ion-beam energy on photo-neutralization efficiency and beam-profile evolution. The results show that the neutralization efficiency increases and then saturates before entering a saturation regime; shorter-wavelength lasers achieve higher efficiency under the same optical power; and increasing ion-beam energy leads to reduced neutralization efficiency due to shortened residence time in the optical field. This work provides an effective theoretical framework for studying high-energy negative ion photo-neutralization, elucidates the coupling between space-charge effects and beam collimation, and offers guidance for the optimized design of photo-neutralizers in high-power neutral beam injection systems.