A three-dimensional Monte Carlo method (3D MCM)-based extinction model is proposed. In this model, the incident light beam is assumed to be composed of discrete photons, and Mie scattering theory is employed to describe how light scatters off individual particles. This approach enables the prediction of a particle system's extinction spectrum by counting all events after photons enter the system. The traditional extinction model, Lambert-Beer (LB) model, is calculated simultaneously, and a measuring device is built to verify the model. The comparison shows a root mean square error of <0.003 between the results of the 3D MCM and LB model, and <0.015 between the results of the 3D MCM and experimental model. These findings confirm the predictive accuracy of 3D MCM for characterizing extinction spectrum, thus expanding its applicability to various scenarios. 3D MCM model is successfully applied to the mixed particle system, and the prediction for extinction spectrum under non-parallel beam incidence is realized.