A highly-integrated multi-antenna array comprising a first conductor layer, a second conductor layer, a plurality of conjoined conducting structures, a plurality of slot antennas, and a conjoined slot structure is provided. The first conductor layer and the second conductor layer are spaced apart by a first interval, and are electrically connected by the conjoined conducting structures. Each slot antenna has a radiating slot structure and a signal coupling line, which partially overlap or cross each other. All radiating slot structures are formed at the second conductor layer. Each signal coupling line is spaced apart from the second conductor layer by a coupling interval and has a signal feeding point. Each slot antenna is excited to generate at least one resonant mode covering at least one identical first communication band. The conjoined slot structure is formed at the second conductor layer and connects with all radiating slot structures.