Abstract: The plant of pebble-bed module high temperature gas-cooled reactor (HTR-PM), one of Chinese National S&T Major Projects, started the first concrete date (FCD) in Rongcheng, Shandong Province. A scale model experiment installation was constructed to verify the mixing performance of the hot gas mixing structure at HTR-PM reactor outlet. The experiments were carried out on the installation which included three series of conditions: Constant flow and variable temperature differences, constant temperature difference and variable flows as well as constant temperature difference and total flow and variable flow ratios. The mixing performance of the hot gas mixing structure is around 98% in all two-channel working conditions according to the data collected in the experiments. By comparing with the requirement of the inlet temperature for steam generator, it is concluded that the hot gas mixing structure at HTR-PM reactor outlet can meet the mixing requirement under two-channel working condition if the leakage out of the reactor core is considered