The invention discloses a polymerized piperylene preparation method, particularly to a process for preparing polymerization-grade piperylene by removing cyclopentadiene from crude piperylene through aselective hydrogenation reaction, wherein a selective hydrogenation reaction is performed by using Pd-Pb/Al2O3 as a catalyst to selectively hydrogenate cyclopentadiene into cyclopentene, and the cyclopentene and the cyclopentane are removed through extraction rectification. According to the present invention, by using the difference in the adsorption rate and the hydrogenation activity between piperylene and cyclopentadiene on the catalyst, the difficultly separated cyclopentadiene in the crude piperylene is removed by the hydrogenation, such that the operation of the process is simple, the cyclopentadiene removal rate is high, environmental pollution is not generated, the piperylene loss is low, and the polymerization-grade piperylene can be prepared.