Abstract: For studying the passively mode-locked character of semiconductor saturable absorber mirror(SESAM),a semiconductor saturable absorber mirror,made by Institude of Semiconductors,Chinese Academy of Sciences,was used to obtain a passivel mode-locked Nd:YAG laser with a simple straight cavity.Stable ps mode-locked pulse train was realized.The mode-locked pulse duration is about 48.2ps measured by autocorrelation.The energy of the train is 24mJ.In addition,the constructure of 1.06μm semiconductor saturable absorber mirror and the theory of passively mode-lock was analyzed.Semiconductor saturable absorber mirror is mainly made up of distributed Bragg reflection(DBR) and saturable absorber.The DBR is made up of different higher and lower refractive index materials.Then the reflection spectrum of different pairs of DBR in semiconductor saturable absorber mirror was simulated,so was the distribution of electric field in DBR.From the results,it can be seen that as the increase of pairs of DBR,the reflectivity of central wavelength also increased;when the pairs is above 13,the reflectivity of central wavelength exceeded 99%.In conclution,semiconductor saturable absorber mirror can replace the traditional passively mode-locked component(such as Cr4+:YAG or organic dye) to be the most perfect component for the mode-lock of solid laser.