Abstract: To investigate the effects of the location and number of beam openings on the mechanical performance of floors under fire, fire tests were conducted on four concrete floors with beam openings. The study results revealed the variation in temperature fields, the displacement curves, and the crack development modes. Based on a traditional yield-line theory, three equivalence principles were proposed to calculate the additional displacement caused by beam openings, viz., deformation equivalence, load equivalence, and internal force equivalence. A modified yield-line theory was established, applicable to concrete floors with beam openings under fire. The study results also showed that the location and number of openings had a relatively minor impact on overall cracking of the floors and beams. The effect of beam openings on the resistance of floors to high-temperature deformation was significant, but the effect of the location and number of openings was relatively minor. Taking into account the vertical displacement and openings of the beams, the ultimate load obtained using the modified yield-line theory was found to be reasonably accurate.