Abstract: In order to study the gain medium,Nd:YVO4,pumped continuously by LD,Cr4+:YAG saturable absorbers and intro-cavity doubling KTP crystal are used in a passive Q-switched green laser. Based on the rate equation of the fore level system and numerical simulation,the relationship of the system parameters and the characteristics of the laser beam are analyzed.The theoretical results conform to the experimental results.It is useful to optimize and select the parameters of such systems.