The partial admission axial turbines operate with the extreme pressure, temperature, and rotational speed for underwater applications. The thermal stress and mechanical stress need to be carefully examined to avoid the operation failure. In this paper, a two-way weakly fluid-thermal analysis is performed to attain the rotor disk temperature distribution. The fluid simulation is performed by solving the three-dimensional Reynolds averaged Navier-Stokes equations coupled with k-omega SST turbulence model, while the thermal analysis is conducted using the finite element method. The mixing plane method is applied when transferring the temperature due to the partial admission configuration. Once the steady state temperature distribution is achieved, the pressure distribution and centrifugal forces are also applied as the aerodynamic and mechanical loads. The corresponding stress and deformation are subsequently obtained. The results show that the maximum stress at the operating point exceeds the allowable material stress, indicating a proper cooling strategy is needed for future investigations.