Variable-section structure of stiff beam and construction method thereof

The invention discloses a variable-section structure of a stiff beam and a construction method thereof. The variable-section structure comprises a section-steel keel, a steel bar skeleton distributed at the periphery of the section-steel keel and beam concrete cast on the outer sides of the section-steel keel and the steel bar skeleton, wherein the section-steel keel is of a variable-section structure and is divided into a first section of section-steel keel and a second section of section-steel keel from a variable-section boundary part; the steel bar skeleton comprises beam-top main bars and beam-bottom main bars; the beam-top main bars are disconnected from the variable-section boundary part and are divided into first sections of beam-top main bars and second sections of beam-top main bars; one end of each first section of beam-top main bar is connected with a stiff column at one corresponding side, and the other end of each first section of beam-top main bar is connected with each vertical connection plat