Abstract: 3,4-Dinitropyrazole (DNP) has excellent performance in energy density and safety, and it is a novel carrier explosive with broad application prospects. In order to study the process and forming law of DNP-based melt-cast explosives, DNP/HMX (40/60) were used as experiment materials, and the method of combining numerical simulation and experimental verification was used to study the effect of riser preheating process on the porosity reduction mechanism of DNP/HMX melt-cast explosives. The influence of riser preheating process on solidification time and charge defects was analyzed, and on this basis, the influence of the forming process in the process of large-scale DNP/HMX melt-cast explosives was studied. The results show that the riser preheating process can effectively reduce the porosity of the charge by changing the internal solidification sequence of the charge and ensuring the continuous action of the feeding channel during the charging process; the size of the charge has a significant impact on the explosive forming process: cooling time increases with model size; at high preheating temperature, the influence of model size on cooling time falls down; under the same process conditions, the larger the model size, the greater the proportion of porosity, and the greater preheating temperature required to eliminate the porosity of the charge; models within D200 mm can eliminate the porosity of the charge by preheating risers, while the porosity cannot be eliminated by the riser preheating process individually above a critical diameter.