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Molecular crystals are complex systems exhibiting various crystal structures, and accurately modeling the crystal structures are essential for understanding their physical behaviors under high pressure. Here, we have performed an extensive structure searches of ternary carbon-nitrogen-oxygen (CNO) compound under high pressure by CALYPSO method and first principles calculations and successfully identified three polymeric CNO compounds with $ Pbam $,$ C2/m $ and $ I\bar{4}m2 $ symmetries under 100 GPa. Most interestingly, these structures are also dynamically stable at ambient pressure, and are potential high energy density materials (HEDMs). The energy densities of $ Pbam $, $ C2/m $ and $ I\bar{4}m2 $ phases of CNO are about 2.30 kJ/g, 1.37 kJ/g and 2.70 kJ/g, respectively, with the decompositions of graphitic carbon and molecular carbon dioxide and $\alpha$-N (molecular $ \rm N_2 $) at ambient pressure. The present results offer in-depth insights into the structural evolution and physical properties of CNO compounds under high pressures, which offer crucial insights for the design and synthesis of novel HEDMs.