This paper focused on a statistical analysis for evaluating creep crack growth rate (CCGR) of Grade 91 steel which is used in Gen-IV nuclear reactors. A series of CCG data was obtained from CCG tests conducted using 1/2” compact tension (CT) specimens under various applied loads at 600 oC. The CCGR was statistically analyzed in terms of the empirical equation between the CCG rate (da/dt) and C* parameter. Three methods such as the least square fitting method (LSFM), the mean value method (MVM), and the probabilistic distribution method (PDM) were compared using the relationships between da/dt and C* parameter, which were obtained using the Monte Carlo Simulation (MCS) technique under various load conditions. It was identified that the predicted data followed the MVM and PDM distribution well. The CCGR of Grade 91 steel could be successfully estimated in the viewpoints of probability.