Poly(1-oxo-2-phenyltrimethylene) was successfully synthesized in the presence of palladium acetate and rare earth acetate $RE(OAc)_3$ (RE=Pr, Nd, Eu, Dy, Ho) multiplex catalyst system. The final products were characterized by elemental analysis, nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The effects of various reaction parameters including molar ratio of rare earth/$Pd^{2+}$, methanol usage, 2,2-bipyridyl, p-toluensulfonic acid, and p-benzoquinone were studied in detail, and the influence of different rare earths on the copolymerization was also discussed. It is found that the rare earths have favorable co-catalytic properties and palladium-rare earth multiplex catalyst showed higher catalytic activity than palladium catalyst in the copolymerization of carbon monoxide (CO) and styrene (ST).