The invention provides a moisture absorption and reconstruction simulation method and system of black carbon cluster particles based on a fractal theory, wherein the method comprises the following steps of building a moisture absorption growth model of black carbon monomers in the black carbon cluster particles according to the moisture absorption growth data of the black carbon aerosol particles; using a DLA model and a moisture absorption growth model to simulate the morphostructure of the black carbon cluster particles; through the matching of the moisture absorption growth data of the black carbon aerosol particles and the simulated morphostructure of the black carbon cluster particles, building a moisture absorption and reconstruction model of the black carbon cluster particles; simulating the moisture absorption and reconstruction process of the black carbon cluster particles by using the DLA model according to the built moisture absorption growth model of the black carbon monomers and the moisture absorption and reconstruction model of the black carbon cluster particles. By using the method and the system, the deformation process of the black carbon cluster particles in damp air can be accurately simulated; the necessary premise can be provided for further and precisely estimating the radiation forcing effect of the black carbon cluster particles.