The invention belongs to the technical field of industrial catalysis of petrochemical industry, and discloses a method for preparing decalin based on the catalytic hydrogenation of tetralin at room temperature, and an organic solvent. The method comprises the following steps: using carbon nanotube-CNTs (activated carbon-AC or carbon black-C) as a carrier to prepare a ternary metal-loaded catalyst (denoted M1/M2M3/CNTs) loaded on M1M2 bimetallic nanoparticles with 0.4-6% Rh (Ir, Pt, Pd, Au or Ru) as nanoscale island, wherein M1 is equal to Rh, Ir, Pt, Pd, Au or Ru; M2 is equal to Ni, Fe, Co or Cu; M3 is equal to Ni, Fe, Co or Cu. The M1/M2M3/CNTs ternary metal-loaded catalyst provided by the invention has tremendous industrialization prospects with 100% decalin selectivity and yield, the adopted catalyst has the advantages of low loading capacity, simple preparation, low cost and good stability, and can be reused for many times.