The invention belongs to an efficient model stage for a centrifugal compressor and specifically relates to a PCL compressor model stage and a design method thereof. The PCL compressor model stage is applicable to the modeling design of PCL compressor products for long-distance pipeline devices. The model stage comprises an impeller, a vaneless diffuser, a curving channel and a backflow device, the impeller is located at the position of an inlet of the model stage, the vaneless diffuser is arranged at the position of an outlet of the impeller, the backflow device is located at the position of an outlet of the model stage, and the vaneless diffuser and the backflow device are communicated with each other through the curving channel. According to the model stage, the machine mach number Mu2 is equal to 0.45, the flow coefficient fai 1 is equal to 0.085, the energy head coefficient tau is equal to 0.52, and the polytropic efficiency eta pol is from 0.87 to 0.88. By means of the efficient model stage, the PCL centrifugal compressor is provided with high operation efficiencies and large working condition ranges.