In the W type cavity,a laser diode-pumped passively mode-locked Yb:YSO laser is demonstrated with semiconductor saturable absorber mirror (SESAM).At the pump power of 13.5 W,the average output pulse power is 2.39 W,and the repetition rate is 104 MHz.The actual pulse width is 3.2 ps,the center wavelength is at 1043.5 nm,and the full-width at half-maximum of the spectrum is 1 nm.