A novel scheme of double-layer optical trap, which is composed of binary π-phase-plate arrays and focusing lens arrays, for trapping cold atoms or molecules was proposed. The double-layer optical trap is formed at the two sides of the focal plane when this optical system is illuminated by plane light wave. The principles of producing the double-layer optical trap were introduced and the relations between intensity distribution as well as intensity gradient and parameters of the optical system were analyzed in detail. Moreover, the optical dipole potential and spontaneous scattering speed, including Rayleigh scattering and Raman scattering, of the atoms or molecules trapped by double-layer optical trap were studied. The scheme can be used not only in trapping atoms or molecules of multiple samples and all optical Bose-Einstein condensation (BEC),but also in preparing novel double-layer 2D optical crystal lattice.