The invention discloses a device and method using pulse accumulation and amplification to realize a high power ultrashort pulse laser. The device comprises a pulse laser beam splitting system, a pulse amplification system, a continuous laser beam splitting system, a carrier envelope phase synchronization system and a balance optical cross-correlation pulse accumulation and amplification system. The method comprises the steps of: splitting the pulse laser into a plurality of paths; respectively amplifying or compressing each path of the laser to obtain a plurality of paths of ultrashort pulses relatively high in power; locking the amplified plurality of paths of ultrashort pulses relatively high in power onto one path by means of frequency beating with a continuous laser device and circuit frequency mixing so as to realize carrier envelope phase synchronization of the plurality of paths of pulse lasers; and finally, performing coherent combination on the plurality of paths of pulse lasers through a balance optical cross-correlation technology, realizing the accumulation and amplification of the plurality of paths of pulse lasers, and outputting the ultrahigh power ultrashort pulses.