Waterproof and flame-retardant building expansion joint structure

The waterproof and flame-retardant building expansion joint structure comprises a first connecting assembly, the first connecting assembly comprises a first base and a second base, the first base and the second base are connected through a sliding rod, and the sliding rod comprises two cylindrical parts and a connecting part connecting the two cylindrical parts; the first base and the second base are embedded and installed in grooves formed in the tops of wall bodies on the two sides of the expansion joint during use, the opposite sides of the first base and the second base are provided with containing grooves for the cylindrical parts on the corresponding sides to be arranged in a sliding mode respectively, and the containing grooves extend in the length direction of the expansion joint; the cover plate is arranged above the first base and the second base in a covering mode, and the cover plate is connected with the connecting part of the sliding rod through an elastic connecting piece; and the second connec