The in-situ reaction is an important method of preparing metal matrix composites: it can produce more uniform distribution of the reinforcement particles and more excellent structure of the phase boundary between the particles and the matrix. Therefore, the kinetics of in-situ reaction process deserves to be further studied. However, as the in-situ reaction is a rapid random process under high-temperature condition, it is difficult to observe the reaction process of metal-matrix composite materials experimentally. In this work, we propose a new phase-field model to describe the in-situ reaction process, and investigate the nucleation kinetic processes of in-situ reaction under different physical conditions. We find that the nucleation rate increases with the augment of curvature radius and noise intensity, and the size distribution of the particles is more uniform under the conditions of a small curvature radius and strong noise. With the increase of the undercooling, the nucleation rate first increases and then decreases, which is consistent with the classical nucleation theory.