A thermal performance test of the horizontal coaxial tube hot gas duct(HGD) for the 10 MW high temperature reactor test module (HTR-10) will be performed on a helium test loop (HETL). The present paper described the technical feature of the HETL and the test section of the HGD. The HETL consists of helium loop, purification, storage and pressure regulation system of helium gas, sampling and analyzing system of trace impurity in helium gas, measuring of parameters, data acquisition and controlling system, et...