In this study, interrupted creep crack growth tests were conducted using C(T) specimen with side-grooves and circular notched round bar specimen of P92 steel. After the interrupted tests, to investigate the creep crack growth and damage progression behaviors of P92 steel under the multi-axial stress field, cross-sectional observations around the notch and crack tip were conducted. From the measurement results of the change of micro Vickers hardness and void area fraction with creep time, it was indicated that the region of low hardness and high void area fraction were existed near the notch or crack tip. Then, three-dimensional elastic-plastic creep analyses were conducted for each specimen. From the results of finite element analyses, the regions of high hydrostatic stress and high tri-axiality factor were in good agreement with the region of high void area fraction for each specimen. This result indicated that the multi-axial stress field contributes to the void formation. Furthermore, the effects of the absolute value and gradient of tri-axiality factor on void formation were discussed.