Using the Spectra Physics Company produced 1. 1 W, 90 fs regenerated mode locked Ti:Sapphire laser as pump source, KTP as nonlinear gain medium, and BBO as a intracavity frequency doubling crystal, we construct a synchronously pumped intracavity frequency doubled fs KTP optical parametric oscillator (OPO). It's output tuning range is from 528 nm to 586 nm, the optimal average output power is 240 mW, and the pulse width is about 100 fs. The oscillation of this OPO system can last for about three hour, even without a feedback system.