One-way FSI with conjugate analysis was performed to study the impact of the adiabatic wall assumption in CFD on the impeller deformation. The displacement and stress at the leading edge increased by 8.4% and 1.8% compared to one-way FSI simulation, respectively. These results came from difference in temperature distribution. The displacement at the blade tip decreased for the increase of blade root thickness. It showed that the increase of the thickness of blade root strengthened the blade rigidity and positively influenced the impeller mechanical performance.