The invention discloses an automatic playing mechanical device and an automatic playing system of percussion to fill in the gap in the prior art. The automatic playing system comprises a music score generator, a control device and the automatic playing mechanical device. The music score generator is used for analyzing musical instrument digital interface (MIDI) music score files to obtain music score information and to generate driving data according to the music score information. The control device is used for generating driving signal output according to the driving data. The automatic playing mechanical device is used for receiving driving signals to produce knocking actions for the playing device. According to the automatic playing mechanical device and the automatic playing system of the percussion, MIDI files can be received, the driving signals can be generated, and the percussion such as xylophones can be played through the signals.