High-pressure and high-temperature(high-P-T) in-situneutron diffraction detection method is a field of growing interest, in particular, for its numerous applications in the field of condensed matter physics, crystal chemistry, geophysics, materials science and engineering. In this work, we design and optimize a set of assembly for high-P-T in-situneutron diffraction experiment in neutron source of China by using Paris-Edinburgh(PE)-type press. The high-P-T experiment is carried out with a high-pressure neutron diffraction spectrometer (Phoenix) of China Mianyang Research Reactor (CMRR). A 1500 KN uniaxial loading system and a 1500 W constant current source provides extreme conditions of high-P-T for PE press. The toroidal anvil we use is made of tungsten carbide. We use two types of gaskets: one is machined from the null-scattering TiZr alloy and the other is made from the thermal insulation ceramic material of ZrO ₂. High-temperature furnace is formed by graphite. First, a simplified simulation analyses of the pressure change rates in different areas of the entire assembly are carried out, and it is concluded that the gasket I, II, III areas are designed with a gradient decreasing method. The compression ratio of the sample chamber is significantly improved. Then when the gasket reaches the same compression ratio, the cell pressure will be higher than the pressure before optimization. After that, we conduct experimental verification on the optimized design. Through a series of optimization experiments for assembly on the rheological control of gasket, the improvement of thermal insulation performance and the maximization of effective sample volume under high-P-T, the key technical indicators and design scheme of the high-P-T in-situneutron diffraction platform are verified. The temperature and pressure in the sample cavity are calibrated by using the MgO's high-P-T in-situneutron diffraction spectrum and equation of state. The in-situneutron diffraction sample cavity environment of the designed platform can reach the conditions of 11.4 GPa and 1773 K. The successful development of this assembly greatly improves the experimental conditions of CMRR high-P-T neutron diffraction platform. At the same time, it has important reference significance for further improving the high-P-T loading conditions of the PE-type press and expanding the application scope of the PE-type press.