Abstract: The in-situ experimental study of the microstructure of materials under thermodynamic coupling under near-working conditions is very important for in-depth understanding of the evolution mechanism of material service performance. The microscopic distribution of nanostructures on the sample can be given. Based on the advantages of small-angle neutron scattering method with good statistics and large sampling volume, in-situ experiments can be carried out, based on the small-angle neutron scattering spectrometer of China Advanced Research Reactor, an in-situ experimental device with simultaneous loading of high temperature and tensile force was designed and developed, and the morphological changes of materials at the nanoscale were measured online at high temperature and high pressure. The test results of the inspection and calibration experiment show that the maximum load of the device can reach 20 kN, the maximum temperature is 800℃, and the temperature control accuracy is better than ±1℃. The device was used to carry out in-situ small-angle neutron scattering experiments on nickel-based single crystal superalloy samples, and the obvious changes in the internal nanostructure of the samples under temperature tension conditions were obtained, indicating that the device could carry out the experimental research ability of in-situ thermodynamic coupling loading small-angle neutron scattering. The device and its corresponding experimental methods can also be used for in-situ experimental research of various high-temperature structural materials such as nuclear power stainless steel to provide microstructure evolution data.