The invention relates to a garbage crushing system and a garbage crushing method. The garbage crushing system comprises a first crushing device and a second crushing device, wherein the first crushing device comprises a box body, the box body comprises an input material port and an output material port, the box body is internally fixedly provided with at least one rotating shaft, and the rotating shaft is provided with crushing rollers; the second crushing device comprises a shell, the front end of the shell is provided with a feed port, the rear end of the shell is provided with a discharge port and discharge openings, a milling smashing piece is placed in the shell, and a right amount of water is added in the shell; and the milling smashing piece in the shell can smash, mill, compress and pierce the garbage in a rotating process of the shell, the garbage is moved on the rear end of the shell in a rotating process, heavy materials are discharged from the discharge openings, and light materials are overflowed from the discharge port. The garbage crushing method provided by the invention has the advantages that the garbage does not need to carry out primary election when the garbage is crushed, the garbage is directly poured into the first crushing device so as to carry out first crush, and then sent in the second crushing device for further crush again, the crush of the whole garbage is realized, and the efficiency of garbage treatment is improved.