The invention discloses a sound source device based on an underwater mobile platform. The sound source device includes an externally-mounted sound source cabin, a mounting mechanism and a multi-electrode emission array mechanism. The externally-mounted sound source cabin is externally mounted and fixed on the underwater mobile platform through the mounting mechanism. The externally-mounted sound source cabin is connected with the multi-electrode emission array mechanism. After the electric energy in the externally-mounted sound source cabin is transmitted to the multi-electrode emission arraymechanism, the electric energy is quickly released and converted into sound energy to excite sound waves. Compared with the sea surface sound source in the prior art, when the sound source device provided by the invention carries out seismic detection in the deep ocean, as the sound source is towed near the sea bottom, substantial attenuation of sound waves (especially high-frequency sound waves)by deep sea water is avoided, the resolution of seismic detection is improved, and the formation penetration depth is increased.