This article describes the application of technology for quenching catalytic pyrolysis gas at the Daqing commercial CPP test unit and the Shenyang commercial CPP production unit. On the basis of results for application of the Shenyang CPP unit this paper puts forward an improved process flow scheme for quenching the pyrolysis gas and made calculations using the process fiowsheet software. Case Ⅰ of the process flow scheme, which is designed for full circulation of slurry, intends to use the pyrolysis light oil and fresh feed oil as the quenching media with the product slurry oil and fresh feedstock being discharged from the quench cooler bottom and routed directly to the reactor so that the fresh feed oil can be preheated prior to pyrolysis. Case Ⅱ of the process flow scheme intends to adopt recycle oil as the quenching medium with the product slurry and recycle oil being discharged from the quench cooler bottom to the fractionator, which then delivers the slurry from the bottom. These two cases for improving the process flow diagram can all effectively control the density and viscosity of the quenching medium to secure the smooth operation of quench cooler.