The invention provides a description method for propagating light in a medium based on a lattice Boltzmann model. The description method comprises the following steps: step one, initializing the size of an organizer, obtaining the positions of a light source and a detector, and setting the organizational parameter of the organizer; step two, exciting a fluorophore to emit fluorescence; step three, using the provided lattice Boltzmann model to simulate the diffusion processes of exciting light and fluorescence respectively; and step four, according to the result obtained in the step three, using a reconstruction algorithm to reconstruct the concentration of the fluorophore in the organizer. The description method can be applicable to establishment and solving of a forward model in the image reconstruction such as optical imaging, photoacoustic imaging, electromagnetic source imaging, microwave imaging and electrical impedance imaging. According to the description method, a novel fluorescence tomography imaging system is constructed based on the model, and compared with a Monte Carlo method, the reconstruction efficiency of the fluorophore is greatly improved; and compared with a finite element method, the computational efficiency is greatly improved on the basis of considerable reconstruction precision.