The essentiality and necessity of pulse shaping to second harmonic generation (SHG) experiment of laser are analyzed. At present, the plasma shutter which has compact structure and good effect on the pulse shaping is a better method by which the high-quality short pulse can be obtained. The plasma shutter in which laser triggering gas breakdown is used to shape the laser pulse is devised. The principle is explained by using reflection and transmission of electromagnetic wave in plasma. Plasma shutter is used to shape the transversely excited atmospheric pressure (TEA) CO2 laser pulse. The TEA CO2 laser pulse with full width at half maximum (FWHM) of 60 ns and the nitrogen tail of several hundred ns is shorten to the pulse with FWHM of 30 ns and free of nitrogen tail. When adding plasma shutter to the SHG experiment using two crystals, the conversion efficiency is 12.9%. This figure is bigger than 2% which is gained without plasma shutter.