Abstract: To further improve the velocity of deep laser drilling in thick metal plate, aiming at 5mm thick stainless steel plate, laser drilling method of long pulse laser with high pulse energy superposed by short pulse laser with high peak power was put forward. The theoretical model of laser drilling by superposed pulsed lasers was established. The function of long pulse laser with high pulse energy was to melt metals, while the removal of metal melted things relied mainly on short pulse laser of high peak power. The drilling effects under different laser parameters (pulse energy, pulse width and drilling method) were studied. The results show that, compared with laser drilling by single long pulse, laser drilling by the superposed pulse can substantially reduce the drilling time. For long pulse of 2ms pulse width and 2.9J pulse energy, the drilling velocity of superposed pulsed lasers increases by 2.3 times while the energy cost reduces 20%. And the larger the pulse energy is, the narrower the pulse width is, the faster the drilling velocity becomes. The study provides a basis for laser selection in laser drilling by the superposed pulsed lasers.