Stimulated by agricultural development, ammonia becomes the second buck chemical in the world, and many ammonia synthesis plants will discharge ammonia-containing wastewater and destroy the ecological balance. In this work, Density Functional Theory (DFT) method was used to study the adsorption characteristic of typical aliphatic boranes on NH3 as well as N2, H2 and CH4. The results showed that the adsorbents could selectively adsorb NH3 over N2, H2 and CH4. The chain length of CH2 has little effect on the adsorption characteristic of boranes while the adsorption energy strongly affected by the number of CH3 groups directly attached to B for boranes. The analysis of Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) indicated that LUMO is contributed by adsorbent and HOMO is contributed by adsorbate. Molecular electrostatic potential indicated that the positive charge of B and the negative charge of N can form the optimal configuration. The selectivity coefficient showed that the adsorbent has high selectivity to ammonia. The desorption of NH3 could be readily achieved by increasing temperature. This study can provide the adsorption mechanism of this system and give a guidance on designing reusable aliphatic borane resin to selectively adsorb and recover NH3.