In this paper,an end-pumped Nd∶Cr4+∶YAG microchip laser with hundreds picoseconds pulse width is reported. Through optimizing the transmissions of YAG∶Gr4+ layer initial and oscillator,gain,length and other parameters,on the repetition of 100 Hz,pulse width of 297 ps,single pulse energy 261 μJ,energy stability better than 0.02 %,optical quality M2=1.45 of the 1064 nm single frequency laser are obtained.