A multi-beam phased antenna structure and a controlling method are provided. The multi-beam phased antenna structure includes a main antenna array and a passive beam forming circuit. The main antenna array includes a plurality of first main antennas and a plurality of second main antennas. The first main antennas are spaced out a predetermined distance. The predetermined distance is related to a coverage of the multi-beam phased antenna structure. The first main antennas and the second main antennas are interleaved. The second main antennas are spaced out the predetermined distance. The passive beam forming circuit includes a plurality of main phase shifters. The main phase shifters are electrically coupled to the second main antennas, such that a difference between a first phase of each of the first main antennas and a second phase of each of the second main antennas is substantially 180°.