The invention discloses a plate spring of interlayer reinforced two-dimensional/three-dimensional braided composite material and a preparation method thereof. A monolayer fabric of different fiber materials is formed by three-dimensional stereo braiding, the monolayer of the special fiber material and in the three-dimensional braided structure is designed on the special part in relatively high rigid or strength requirements, and finally the layers are vertically seamed to make the laminated monolayer structure form a whole body. Finally, the fabric of the two-dimensional/three-dimensional composite structure and resin are repeatedly soaked and composited through a resin vacuum transfer moulding technology, and the novel automobile plate spring of composite material which is high in strength and rigidity, small in deformation amount, large in fatigues resistance, long in service life and high in high-low temperature environment adaptability is prepared through gradient heating and curing. The plate spring uses the novel structure and the structure form to satisfy the use requirements of different loading capacities especially automobiles with heavy loads, and the problems such as interlayer fracture caused by relatively low fatigue load strength of the common plate spring of two-dimensional laminated structure composite material are conquered.