Thermoregulated phase-separable Ru3(CO)12/PETPP (PETPP=P[p-C6H4O (CH2CH2O)n H]3, n=6) complex catalyst was first applied in the hydrogenation of styrene. Under the conditions: P(H2)=2.0MPa, T=90(C, styrene could be completely transferred and the yield of ethylbenzene reached up to 99.5%. After simple decantation, the catalyst could be reused for ten times without decreasing in activity.