A new picosecond pulse laser consists of a resonator, a single pulse laser selector, two amplifiers, frequency doubling, and so on. A Nd∶YAG rod is used as active medium of laser and two Glan prisms are separately used as polarizer and analyzer of polarized light. In order to generate a series of mode-locked pulse laser lights, a passive mode-locked dye cell is used in the resonator. A single pulse laser light is obtained from the series of mode-locked pulse laser lights after they have passed the selector. Finally, after the pulse laser light has been amplified and doubled in frequency, an output of laser light beam with energy of 120 mJ and duration of laser light of 100 ps at wavelength of 532 nm is realized. It is equal about 1.2×109 W of pulse power or 4.2 ×109 W/cm2 of power density. An out-triggering synchro-precision of better than 2 μs is obtained from the laser.