The disclosure relates to the technical field of building materials, and in particular, to lightweight aggregate ultra-high performance concrete (UHPC) and a preparation method thereof. The lightweight aggregate UHPC provided in the disclosure is prepared from the following components in parts by weight: cement 220-260 parts; silica fume 100-120 parts; expanded perlite powder 120-160 parts; expanded perlite 230-260 parts; polycarboxylate superplasticizer 15-20 parts; steel fiber 76-93 parts; and water 140-160 parts, where a maximum particle size of the expanded perlite powder is 0.075 mm; and a particle size range of the expanded perlite is 0.075-0.6 mm. The lightweight UHPC prepared according to the design of the disclosure has excellent density performance, and can satisfy requirements of concrete components, etc. in service in super-long-span bridges, super high-rise buildings, and complex marine environments for lightweight, ultra-high strength, and ultra-high durability of cement-based materials, and has a relatively high promotion value.