Abstract: In this paper, a binary diffractive small lens array (SLA) which can be fabricated easily, is introduced and designed for focal plane imaging in W wave-band. Comparing with common refractive SLA, the designed two-step binary diffractive SLA is easier to fabricate. The hybrid numerical method combining of geometrical optics/ physical optics and FDTD,is adopted to analyze the coupling between the diffracted field in the focal region of the objective lens and SLA. The hybrid numerical method has also been verified by the relative experimental results. Simulated results show that, the diffractive SLA has good imagine performance.