We have developed a nanosecond pulse width Q-switched stretched 532-nm Nd∶YAG green laser based on a multipass cavity (MPC). The pulse widths were stretched from an adjustable regime of 110--260 ns to 460--600 ns by changing from single-pass to multipass operation at a pulse repetition rate of 10 kHz. At a typical pulse width of 460 ns, an average output power of 6.5 W at 532 nm was successfully achieved. The 532 nm output power and pulse width versus input power at 1064 nm were simulated. The simulated results were shown to be consistent with experimental data. Such nanosecond pulse lasers are interesting for both industrial and scientific applications, such as laser damage experiments for the development of new materials.