The systematics charaters of the (n,T) and (n,3He)reaction cross sections have been studied. On the basis of odd-even effect, the systematics formulae of the reaction cross sections are obtained as σu,q=(A1/3+1)2aexp[β(N-Z+δ)/A]. A set of fitting empirical para meters by using the least square method are extracted. For the (n,T) reactions, α and β values are 327.602, 9.592 and -24.495,-14.038, respectively; for (n,3He) reactions, α and β values are 0.918 and -11.340, respectiv ely The (n, T) and (n, 3He) reaction cross sections of some nuclei are calculated by using the theoretical model, and a good agreement with existing data are obtained. In addition, the Ω-value effect and possible reaction mechanism are also discussed.