The effect of LD end2pumping and passive Q2switching with Cr4 + ∶YAGon laser mode is studied ;We also discuss the reason ,mechanism and conditions of single longitude mode output from a LD end2pumped and passive Q2 switched laser. In the experiment ,single longitude mode laser pulse of 30μJ energy and 6ns FWHM with 2kHz repe2 tition are acquired.