Cold-formed thin-walled steel concrete composite floor is fabricated with profiled steel sheet-concrete composite slab at the top and cold formed steel built-up beam at the bottom, when fire occurs on the lower side of the floor, the cold-formed thin-walled steel beams and profiled steel sheets will be directly exposed to fire. In order to improve the fire resistance of the floor, a new type cold-formed thin-walled steel concrete composite floor is proposed by fixing fireproof board on the lower flange of cold-formed steel beams to form a fire protection layer. However, the temperature distribution, deflection and fire resistance time of the new floor will change after adding fire protection, so fire resistance performance of the new floor needs to be studied. A simplified three-dimensional finite element model is established to analyze the influence of concrete slab thickness, beam height, load ratio, fire protection on the fire resistance of the new floor. It is found that the temperature at the same height of the steel beam is basically similar along the span direction but not uniform along the height direction when the direction of the profiled steel sheet is vertical to the steel beam. Increasing the thickness of concrete slab has little effect on fire resistance. In addition, the critical temperature of the hot flange with different cross-section sizes under the load ratio of 0.2-0.5 and the time-temperature curves of the hot flange with different fire protection are obtained, which can be used to estimate the fire-resistance time of the new floor.