The properties of magnetic material of Nd-Fe-B are highly affected by various factors such as particle size, magnetic anisotropy, phase purity and crystal structure. Incorporation of excess neodymium was carried out in various percentages so that it will adjust the proportion of neodymium in the host crystal after reduction treatment and finally help to improve magnetic property of a material. The interdiffusion of Nd-Fe and boron was studied for various compositions and their effect on magnetic property was understood with theoretical concepts. The factors such as amount of hard and soft phase in the reduction treated product is also responsible for the possible exchange coupling between hard and soft phase magnets for better magnetic properties.