A single axial and transverse mode Q-switched pulsed laser system is demonstrated based on injection seeding and fast resonance detection technique combined with self filtering unstable resonator. 600 mJ energy at 1064 nm and 300 mJ energy when frequency-doubled, are achieved at Fourier-transform limit and with a beam divergence near diffraction-limit. The system is also characterized by the long-term stability in high vibration environments. The influence of injection-seeding on giant pulse setup time, beam-spot mode, and energy is observed experimentally. The perfect laser radiation is desirable in the area such as nonlinear optics, optical synthesized aperture and high-resolution spectroscopy.