Fe_72-xNd₇B₂₁Nb_x(x=0~4.0)bulk alloys with diameter of 2 mm were fabricated by copper mold casting. The influence of Nb addition on the glass forming ability, crystallization and magnetic properties have been investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), vibrating sample magnetometer (VSM) and physical property measurement system (PPMS). The results show that appropriate addition of Nb can improve the glass forming ability. The fully amorphous ingots are obtained when Nb content is 2.0 at%, 2.2 at% and 2.5 at%. Nb is found to be effective in adjusting the alloy composition and decreasing the volume fraction of paramagnetic Nd_1.1Fe₄B₄ phase . When Nb content is 2.5 at%, the alloy exhibits optimal hard magnetic properties with the remanence (B_r) of 0.63 T, intrinsic coercicity (H_ci) of 448.97 kA/m and maximum energy product ((BH)_max) of 4.54 MGOe. The enhanced magnetic properties can be abscribed to the strong exchange coupling among grains and and high remanence.