We demonstrate a stable compact passively Q-switched laser generating 40 μJ, subnanosecond (< 1 ns) duration, 1064 nm pulses at a repetition rate of 10 kHz. With a composite Nd:YAG/Cr4+:YAG crystal in a simple and compact resonator end-pumped by intense 808 nm pulse, we effectively improve the stability of output laser pulses corresponding to the interpulse amplitude instability less 1% (rms) and the period jitter less 1 μs. These measured pulse-time characteristics agree with numerical simulations and the beam is close to the diffraction limit, with M2 < 1.2. The excellent optical properties and structure make this laser to be an attractive source for high-resolution 3D imaging radars or other widespread applications.