Abstract: High-strength aluminum alloy has the advantages of low density, high strength, and good thermal processing performance. It is the main structural material in the aerospace field. The development of modern aerospace industry has put forward higher requirements for the strength and comprehensive performance of high-strength aluminum alloys. The research and application of dual-phase nanostructured aluminum alloys are inseparable from accurate and reliable phase diagram information. Phase equilibria of the Al-Ni-Er ternary system at 400 ℃ were experimentally investigated through X-ray diffraction, scanning electron microscopy and electron probe micro-analysis. ①New ternary compounds τ₁₁-AlNiEr₄, τ₁₂-AlNi₆Er₁₃ and τ₁₃-AlNi₂Er were discovered in the equilibrated alloy samples. ②Compounds τ₅, τ₁₀, τ₁₃, AlNi₃, AlNi, Al₃Ni₂, Al₂Er, ErNi₂ and ErNi₅ have a certain range of solid solubility. The solid solubility of Ni in Al₂Er is 8.93 at.% and the solid solubility of Al in ErNi₂ is 2.00 at.% at 400 ℃. ③Experiments have verified that CaCu₅-ErNi₅ is a continuous solid solution and the maximum solubility of Al is up to 33.33 at.%.