Quantum well FPA with grating coupling structure is hard to fabricate while the reflective structure is easier when the pixel is small. To confirm that whether the RC structure can take place the GC structure, we simulate the performance on anti-optical crosstalk of the Quantum Well FPA with GC structure or the RC structure by the FDTD software MEEP when pixel’s size is under the diffraction condition, and we prove that the RC structure shows better performance when the size of FPA’s cell is between 5-6.5μm and 8.5-10μm while the GC structure performs better when the cell size is between 6.5-8.5μm and 10-12μm, and these 2 kinds of structure show the close performance when the cell size is between 12-15μm And we have figured out that how the reflective angle, etch depth and the period of the quantum wellinfluence the the FPA’s ability of fight against the optical crosstalk with the RC structrue and a15μm cell size.