The initiation and subsequent decomposition mechanisms of α-RDX crystal under high temperature (3000 K) coupled with detonation pressure (34.5 GPa) were studied by ab initio molecular dynamics simulations. The crystal structure of RDX was relaxed using two types of van der Waals corrections such as PBEG06 and PBETS functional at ambient conditions. The results indicate that the PBEG06 functional is much suitable for studying α-RDX. Results show that the decomposition of α-RDX is triggered by the homolysis of the C—H bond. The DOS clearly validates that the C—H bond is broken. The elimination reaction of HONO during the decomposition is observed. The primary reactions for producing NO₂, NO, N₂O, N₂, HONO, N₂O₄, H, O—H, H₂O, and CO₂ occur at very early stages. After the initiation of RDX, there are three different subsequent decomposition pathways. There are three main interesting subsequent decomposition paths include: (1) the C—N bond hemolysis triggers the other C—N bonds of this ring to break; (2) the dissociation of N—NO₂ bond releases NO₂ gas; (3) the H radical attacks the O atom to release O—H radical by forming O—H bond.