Modularized tower top steel beam and assembling method

The invention relates to a modularized tower top steel beam and an assembling method, the steel beam comprises a plurality of first cross beams, a plurality of second cross beams and a plurality of longitudinal beams, the first cross beams and the second cross beams are consistent in length, width and height, the length of each of the first cross beams and the second cross beams is L, the value of L is 2m-3m, and cross beam joints are respectively arranged at two ends of the first cross beams and the second cross beams in the length direction; longitudinal beam connectors are arranged on one sides of the first cross beams and the second cross beams in the width direction and are symmetrically arranged along the vertical center line, longitudinal beam connectors are arranged at the two ends of each longitudinal beam respectively, the first cross beams are connected with the adjacent first cross beams or second cross beams through the cross beam connectors, and the second cross beams are connected with the adja