In order to increase the energy of the secondary reaction of composite explosives， the novel composite oxidant ammonium perchlorate （AP）-lithium perchlorate （LiP） was prepared by solvent evaporation method. Scanning electron microscope （SEM） and X-ray diffractometer （XRD） were used to test and characterize the morphology， and crystal structure of the sample. The thermal decomposition properties of the samples were analyzed by differential scanning calorimetry （DSC）. The underwater explosion power parameters of three polymer bonded explosives （PBXs） containing composite AP-LiP， mechanical mixture AP-LiP and AP were evaluated by electrometric method. The results show that， for composite AP-LiP， the crystal morphology is fairly regular， the crystal surface is smooth， the particle size distribution is fairly uniform， and no agglomeration is observed. Composite AP-LiP has a high degree of crystallization and a fairly complete crystal structure. The thermal decomposition performance of composite AP-LiP is better than that of mechanical mixture AP-LiP. The underwater explosion results show that， compared with the AP-containing PBX， the shock wave energy， bubble energy， and total energy of underwater explosion of PBX containing composite AP-LiP increase by 0.098-0.154， 0.254 MJ·kg^-1 and 0.352-0.408 MJ·kg^-1 respectively， and the energy decays slower as the distance increases.