The available experimental data on boron particles agglomeration during combustion of boron-containing solid propellants and a mechanism of the boron particles agglomeration are discussed. The model and the method of direct numerical simulation of the boron particles agglomeration have been suggested and developed. The calculation consists of two stages: the first stage is a simulation of a heterogeneous structure of solid propellant; the second stage is a calculation of a behavior of each boron particle, taking into account its interaction with other particles and with flow of gaseous combustion products of solid propellant. A mechanism of the adhesive bonds between the boron particles is suggested and the criterion of conglomerate detachment from the burning surface has been determined. The dependence of the strength of the adhesive bonds between the boron particles on the propellant burning rate and pressure is analyzed. The calculations of the boron particles agglomeration, which demonstrates the effect of the strength of adhesive bonds between boron particles on the intensity of agglomeration, have been carried out.