Spherical AlN powders with micrometer size have attracted great attention owing to their good fluidity and dispersity. However, the industrial preparation methods usually require high temperature and long soaking time, which lead to the high cost and limit the wide application of the products. Herein, nearly spherical AlN particles with the average size of 2.5 µm were successfully synthesized via an in-situ combustion synthesis method. The effect of N2 pressure, NH4Cl content and Al particle size on the combustion reaction procedure, phase composition and microstructure of the products was systematically investigated. The results showed that the decreased N2 pressure, increased NH4Cl content and Al particle size led to the decreasing of combustion temperature and speed, which further affected the morphology of the products. As a result, low N2 pressure (0.2 MPa), a small amount of NH4Cl (0.5 wt%) and fine Al particles (~ 2.5 µm) contributed to a moderate combustion temperature and facilitated the formation of nearly spherical AlN particles. In addition, based on the gas-releasing assisted quenching experiments and thermo-kinetic analysis, a two-step growth mechanism for the nearly spherical AlN particles was rationally proposed. The present method shows the advantages of low cost and high efficiency for preparing nearly spherical AlN particles, which can be used as raw materials for electronic substrates and fillers for packaging materials.