The invention discloses a reactor primary loop coolant flow field, temperature field and stress field coupling calculation method. The method comprises the following steps: 1) constructing a high-temperature gas cooled reactor core model and a steam generator model with the same size as actual equipment; 2) establishing a computational domain 1, a computational domain 2 and a computational domain3; 3) setting equipment materials and fluid domains in the computational domain 1, the computational domain 2 and the computational domain 3; 4) setting areas and boundary layers of a flow field, a temperature field and a stress field; 5) meshing the flow field, the temperature field and the stress field; 6) adopting a k-epsilon turbulence model in the computational domain 1 and the computationaldomain 3, and adopting a porous medium model in the computational domain 2; 7) obtaining flow field, temperature field and stress field distribution results of the computational domain 1, the computational domain 2 and the computational domain 3, and 8) obtaining optimal operation parameter configuration of the high-temperature gas cooled reactor at different power levels. The method can realize coupling numerical simulation calculation of the coolant flow field, the temperature field and the stress field of a reactor primary loop.