A passively mode-locked Nd:YAG laser with a partially reflective semiconductor saturable-absorber mirror is reported.According to the well known ABCD matrix theory,the astigmatism and the stability in the cavity of the laser are theoretically analyzed.Stable continuous-wave mode locked pulses are achieved with a Z-type resonator.The average output power of 372 mW is obtained with the incident pump power of 7.7 W.The pulse duration is measured to be 8.9 ps with a repetition rate of 54 MHz at the central wavelength of 1064 nm.