In order to look for a cheap compact laser source for a micro pulse lidar to remotely sense aerosol and cloud in the troposphere, the studies of diode pumped, Cr4+:YAG passively Q switched Nd:YAG lasers were present. Using different laser cavities with different initial transmissions of Cr 4+:YAG, the output properties of laser were demonstrated. The output energy of 20 μJ per pulse and the repetitive frequency of 2.8 kHz were generated by a LD with 1.1 W and a Cr4+:YAG crystal with an initial transmission of 82%, which it can match the requirement of micro pulse lidar. The measured CW output power and pulse repetitive frequency were consistent with the results of theoretic calculation well.