Disclosed is an ultra-thin speaker comprising: a housing; and a magnetic circuit system therein; a vibration system comprising a cone assembly and a voice coil, the cone assembly having a taper ≤25°, a peripheral edge thereof connected to the housing, and a middle part thereof having a through hole, the voice coil is fixedly connected at an edge of the through hole, the voice coil surrounds and is suspended around the magnetic circuit system, being able to vibrate by an action of the magnetic field generated by the system when a sound signal is introduced; and a dust cap assembly comprising a dust cap body, a central region of the dust cap body is fixedly connected to the system, and an edge region of the dust cap body is connected to the cone assembly and is able to expand and contract along with the vibration of the cone assembly.