To address the longitudinal shear capacity of composite slabs，this paper finds a kind of interlocking effect existing in a new type of composite slab, which is a new kind of shear mechanism and expounds its mechanism. In order to verify the effectiveness of this type of shear mechanism, monodirectional pseudo-static tests for six composite specimens with three kinds of structural forms of the precast panel were conducted. By comparing the integral behavior of the composite slab in ultimate load, hysteric curve, self-resetting property and so on, the results indicate that, when compared with ordinary prestressed concrete composite slabs, owing to its less damage accumulation in the lamination of this new type of composite slab, the proposed interlocking effect can enhance the deformation recovery performance to some extent and ensure that the composite slabs have good interaction between the laminated layer and the precast panel to give full play to its ultimate load.