The time delay of interferometric autocorrelation trace of femtosecond pulse was calibrated in frequency domain. By virtue of the calibrated interferometric aut ocorrelation trace, root-mean-square width and chirp parameter of the femtosecon d pulse to be measured were calculated. Based on these parameters, the Ti:sapphi re oscillator was optimized to generate 115fs pulse in full width at half ma ximum, which was very close to the width of the transform-limited pulse. The mea surement involved only an integration and a fast Fourier transform. Consequently , real-time chirp diagnostics for Ti:sapphire oscillator was feasible.