The invention relates to a double-soundboard sound source structure of a grand piano. The structure comprises a bent back, a main soundboard, a plurality of main ribs and a main back column, wherein the main soundboard is mounted on the upper surface of the bent back; the plurality of the ribs are mounted on the lower board surface of the main soundboard; the main back column is mounted below the main soundboard and forms a gap with the lower surface of a main rib; an auxiliary soundboard is mounted below the main back column through the bent back; the auxiliary soundboard is parallel with the main soundboard; a plurality of auxiliary ribs are mounted on the upper board surface of the auxiliary soundboard; corresponding counter bores are formed in the main ribs and the auxiliary ribs; the main soundboard and the auxiliary soundboard are inserted into sound columns through the counter bores in the main ribs and the auxiliary ribs and are connected with each other. The double-soundboard sound source structure changes the sound source structure of the traditional piano in sounding principle, realizes the effect of resonance of cavities of two soundboards, and has the characteristics that the structure is simple, the vibration performance is good, sound is sustained for a long time, the resonance effect is good, the musicality of the piano is improved, and the sound emitted by the piano has more layers.