In this study, to qualify the constraint effect on creep crack initiation, the correlation analysis between proposed constraint parameter Q’ using time-dependent creep crack-tip stress and creep crack initiation time variable Ai was performed. Ai implies the influence of constraint effect on creep crack initiation. The procedure to calculate the Ai and the Q’-parameter was presented. To evaluate various status of constraint effect, creep crack growth tests for twenty-one compact tension specimens of Type 316H stainless steel at 550°C were investigated. The results of correlation analysis explain the reason for the different initiation time at the same C* level in respect of constraint effect.