Studies on ethylenediamine (EDA) coating pure boron were neglected in many cases previously. Density functional-based first-principle calculation methods as well as reactive molecular dynamics methods are applied to study the mechanism of coating EDA molecules on pure α-phase boron nanoparticles (BNPs). Our calculations predict that there are two stable adsorption configurations for amino groups on α-phase boron periodic slab. The methods of the two adsorption configurations are both chemical adsorptions. In addition, the adsorption behaviors of EDA solution system are not a simple chemical adsorption. It is found that some amino groups were detached from the molecules during the adsorption process. The charge distribution and radial distribution function indicate that new B-N bonds and B-H bonds are formed. The peripheral EDA molecules are adsorbed on the outer side by non-bonding forces. The adsorption curve shows that an organic coating is formed on the surface of boron particles after adsorption. Finally, the analysis of atomic displacement and charge distribution indicates that the internal boron atoms maintained good stability and high activity.