The invention relates to a precast arch hollow brick and a small beam cast-in-situ integral floor structure thereof. The precast arch hollow brick comprises a base, a top cover and connection side surfaces which are connected between the base and the top cover, and the base, the top cover and the connection side surfaces are integrated; the cross section of the base is in a U shape, and two vertical edges of the U-shaped base are folded outward to form horizontal overturning edges; the cross section of the top cover is in an arc shape, and the ends of two sides of the arc top cover are beyond the ends of the horizontal overturning edges on two sides of the base respectively and are aslant located above the horizontal overturning edges; the connection side surfaces are aslant and outward gradually arranged from bottom to top, the bottoms of the connection side surfaces are connected with the ends of the horizontal overturning edges, and the tops of the connection side surfaces are connected with the ends, corresponding to one side, of the arc top cover. According to the precast arch hollow brick, the technical problems are solved that most concrete floor structures at this stage are high in self-weight, low in heat preservation and thermal insulation effect, low in sound insulation effect, complex in construction technology and low in material use ratio; the technical problems are also solved that a precast hollow plate floor is low in integrity and floor cracks are easily caused.