The magnetic properties of Nd-Fe-B alloy magnet powders produced by the HDDR process were found to depend strongly on the hydrogen pressure. Anisotropic magnet powder is obtained by treatment at low hydrogen pressure, whereas isotropic magnet powder is obtained at high hydrogen pressure. Since the reaction rate is determined by the hydrogen pressure and the composition of Nd-Fe-B alloys, it is considered that the appropreate reaction rate of Nd-Fe-B and hydrogen in the disproportion step is the essential factor to induce anisotropy in the magnet powder. On the basis of the result, we established an improved HDDR process (d-HDDR) consisting of four processing step. Nd-Fe-B magnet powder treated at a hydrogen pressure of 0.03 MPa in the d-HDDR process has Br of 1.38T, iHc of 1122kA/m, and (BH)max of 342kJ/m³.