In prefabricated buildings, steel truss composite slabs are widely used as the main force-bearing components. However, the baseplate often cracks before installation on the site, which makes the composite slabs unusable. In this paper, a new type of two-way steel truss composite slab has been proposed, which installs additional transverse steel support on the traditional reinforced truss composite slab, thereby improving the flexural bearing capacity of the composite slab. In order to investigate the effect of the installed transverse steel truss on the cracking state and mechanical characteristics of the composite slab, static loading tests were carried out on the two-way steel truss composite slab baseplate and the ordinary one-way steel truss composite slab floor. The variation rules of the cracking moment, crack distribution, mid span deflection and strain with loads were obtained through the tests. The results show that, under the same load, compared with the traditional one-way steel truss composite slab, the cracking moment of the two-way steel truss composite slab baseplate is larger, the cracks develop more slowly, and the mid-span deflection and strain are smaller. The two-way steel truss can significantly improve the anti-cracking performance of the composite slab baseplate and effectively control the crack development.