Abstract: The effects of Co and Al on magnetic properties and microstructure of Nd-Fe-B alloys are studied in this paper. A magnet with energy product of 278.6~318.4 kJ/m³ (35~40 MGOe) and reversible temperature coefficient (α), of -0.06~-0.08%/K at 293~373 K is abtained. Cobalt atoms enter in the tetragonal phase, increasing Curie temperature and decreasing the reversible temperature coefficient. A new phase Nd(Fc, Co)₂ with MgCu₂ type structure forms in the alloy containing higher Co content. It causes the decrease of the coercivity. Alumium atoms are mainly in the tatragonal phase, it makes the grains become smaller, and rises the coercivity of the alloy. When Al content further increase, a new phase forms, which destroy the coercivity of the alloys.