In this letter, we systematically investigated the temporal and spectral characteristic of ultra-broad band Ti:sapphire oscillator in femtosecond regime. Pulse formation in temporal regime was observed while the spectral shape evolved fro m hyperbolic secant shape into multi-peak one and the bandwidth increased from 40 to 180nm. Experimental results showed that pulse shortening mainly occurred n ot at its bottom part but at its central section while the spectrum was broadene d, and at the same time the relative energy at the bottom part increased.