A gradient nursing solidification method based on layer by layer and sequential solidification principle was proposed to solve the defects such as gas hole and shrinkage hole of charge. By dividing a small section along the axial direction of the charge shell, find out the section most prone to charge defects, control the rising speed of the cooling liquid level and other means to make the solidification of the liquid medicine in this section free of defects, complete the defect free solidification of the liquid medicine in all sections, and obtain a high-quality grain without obvious charge defects; The technical scheme was verified by the gradient nursing solidification application of a DNAN based on melt cast explosive. The charging results show that the scheme can obtain high-quality grain without visible shrinkage, porosity and other defects, and the charging quality is reliable.