The invention discloses a casting-curing insensitive high-explosion-heat explosive which comprises the following components in parts by weight: 65 parts of hexogen, 21.5 parts of aluminum powder, 6-8 parts of binder, 2-3 parts of insensitive agent, 2.5-3.2 parts of plasticizer and 0.5-0.7 parts of curing agent. The hexogen is subjected to grain composition to improve explosive energy. The invention further discloses a preparation method of the explosive, which comprises the steps of batching, mixing, vacuum treatment and vacuum casting, and heating curing. The explosive has a higher explosion heat value, has good viability in hazardous environments such as shock, high temperature, bullets and detonation waves, and has the characteristics of high work capacity and high safety; and compared with PBXN-109 (plastic-bonded explosive-109), the solid content is higher, and the overall properties are equivalent.