Embodiments of the present invention pertain to the field of communications technologies and disclose a multi-band antenna and a communications device. The multi-band antenna includes a reflection panel, at least one high-frequency unit, and at least one low-frequency unit. Each high-frequency unit includes a balun structure, a coupling structure, and a radiation arm structure. The balun structure includes two balun sub-structures, the coupling structure includes two coupling sub-structures, and the radiation arm structure includes two radiation arms. The high-frequency unit and the low-frequency unit are disposed on the reflection panel. Each coupling sub-structure is separately electrically connected to one balun sub-structure and one radiation arm. The coupling sub-structure is configured to transmit a signal whose frequency is higher than a preset threshold, and block a signal whose frequency is lower than the preset threshold.