The eutectic compositions of four ternary systems of energetic materials (including Tetryl/PETN/RDX, AK/EDD/NQ, AK/EDD/NTO and AK/HDD/NTO) were obtained by constructing a special phase diagram for correlation of the apparent fusion heat with the composition (HX-phase diagram). The results obtained from the HX-phase diagrams were confirmed by the determination of the "melting out eutectic" of these systems using HPLC or UV spectrophotometry.