In starting-up turbines of power plants, the procedures recommended by manufacturer should be carefully observed. however, many utilities often start turbines so fast to cause accelerated crack growth. Hence, to accurately predict crack growth life of turbine rotors, a crack growth prediction model is needed in which crack growth rate change due to variation of load increasing time is considered. In this study, using a typical rotor steel (1Cr-1Mo-0.25V steel), creep-fatigue crack growth tests were performed at 538℃ under triangular and trapezoidal waveshapes with 0.5, 1, 10, 100 second load rise times and 100 second load hold time. The effect of load increasing time on the crack growth rate during the succeeding load hold period was investigated from the test results and a new C_t estimation equation was proposed which considers the observed effects. The effectiveness of the proposed equation was verified by showing that the scatter band of the measured (da/dt)_(avg) data was reduced when the new equation was adopted