laser diode (LD) end-pumped Cr 4+: Nd 3+: YAG co-doped microchip laser with 1.1 mm-cavity length is developed, which can achieve very stable output pulse sequences with 6 ns-width, almost 18 mW average power and 1～10 kHz repetition rate. Theoretical analysis is given out and an expression for pump threshold-power is derived. The calculated results are in a good accordance with experimental data