The present invention provides a coaxial speaker including a supporting ring, a magnetic circuit system, a first vibration system, and a second vibration system. The second vibration system locates coaxially with the first vibration system. The first vibration system includes a first diaphragm and a first voice coil. The second vibration system includes a second diaphragm and a second voice coil. The first diaphragm is used for generating treble sound, the second diaphragm is used for generating bass sound. The supporting ring includes a first end portion, a second end portion, and a connecting portion. A projection of the first diaphragm is partially overlapped with a projection of the second diaphragm along a vibrating direction of the coaxial speaker. The treble diaphragm design uses a Z-axis direction vibration space of the bass diaphragm to increase the vibration area to improve the performance.