The band structures, density of states (DOS), and magnetic properties of wurtzite Mn-AlN and Cr-AlN were studied using density functional theory (DFT) with the generalized gradient approximation (GGA) for the exchange-correlation potential. The results indicate that the half-metallic gap of Mn-AlN and Cr-AlN decreases as the Mn/Cr doping concentration increases. This probably results froman increase in the interaction between Mn and Mn or Cr and Cr atoms and a decrease in the hybridization of Mn/Cr 3*d* and N 2*p* states with increasing the Mn/Cr doping concentration, which results in a smaller spin-exchange splitting so the half-metallic gap is reduced. Additionally, with the same doping concentration, the half-metallic gap of Mn-AlN is larger than that of Cr-AlN. This is due to the lower Mn 3*d* states compared to the Cr 3*d* states and the hybridization of Mn 3*d* and N 2*p* states being stronger in Mn-AlN, which leads to a larger spin-exchange splitting so the conduction band minimum of the down spin bands moves far away fromthe Fermi level and the half-metallic gap of Mn-AlN becomes larger.