A multi-antenna mounting device includes: a mounting member to which two or more antennas are fixable; and a tilt angle adjusting mechanism including an upper adjusting component and a lower adjusting component spaced apart along a length direction of the mounting member. The upper adjusting component includes a plurality of tilt angle adjusting holes arranged in a row, one end of the upper adjusting component is connectable to the mounting member, and the other end is connectable to a user's support pole with a fastening element extending through one of the tilt angle adjusting holes. When the fastening element extends through different tilt angle adjusting holes, the multi-antenna assembly has different mechanical tilt angles relative to the support pole. The lower adjusting component includes a first section and a second section. The second section has a predetermined length and the first section is pivotable relative to the second section.