A passively Q-switched Nd∶YAG/Cr 4+∶YAG microchip laser with a low time jitter and a high repetition rate is reported, which uses a single-tube laser diode with a wavelength of 808 nm as the pumping source. Based on the polarization orientation characteristic of a Cr 4+∶YAG crystal with a cutting direction of [001] at a certain incident beam power density, the polarized pumping method is chosen to make the polarization direction of the pumping light parallel to the crystallographic axis direction and all of the residual pumping light after absorption by the Nd∶YAG crystal is used for bleaching the electric dipoles along the crystallographic axis direction of the Cr 4+∶YAG crystal. The results show that the output pulse time jitter of the Nd∶YAG/Cr 4+∶YAG passively Q-switched microchip laser can be effectively reduced with the optimization of the orientation of the Cr 4+:YAG crystal with a cutting direction of [001] when the polarized pumping method is adopted.