Ni2MnSb Heusler alloy is modelled and its magnetic properties are investigated by means of the effective field theory (EFT) developed by Kaneyoshi. Furthermore, the structural and electronic properties are performed by using density functional theory (DFT). According to DFT, with the help of volume-energy optimisation curves, the ferromagnetic (FM) state is more stable in energetic than the non-magnetic (NM) state. The value of the lattice constant obtained in this stable FM phase is a (DFT) =6.03 angstrom which confirms the experimental results reported by Ak et al. (a (Exp) = 5.9861 angstrom). According to EFT, we obtain a bridge constant (k(b) ) for fitting the theoretical and experimental results of Ni2MnSb as k(b) =127.5. When k(b) < 127.5, the theoretical results are smaller than the experimental results. But, when k(b) > 127.5, the theoretical results are higher than the experimental results of Ni2MnSb. However, when k(b) = 127.5, the theoretical results and experimental results are very close to each other and they are almost fitting. Additionally, we find the surface Manganese atoms (Mn2) are the bridge atoms (a(b) ) for fitting the theoretical and experimental M-T results of Ni2MnSb Heusler alloys.