This paper presents a study of crosstalk evaluation of a non-blocking banyan switch fabric based on acousto-optic tunable filters (AOTFs). The non-blocking banyan switch fabric is based on the basic unit of 1×2 AOTFs. After describing the crosstalk that exists in the non-blocking banyan switch fabric based on 1×2 AOTFs, we place our emphasis on the two kinds of crosstalk of them: the accumulated AOTF's coherent crosstalk, and the first-order crosstalk caused by the lack of multiplexers. Analyzing the BER degradation induced by these two kinds of crosstalk, we give the theoretical expression of BER and power penalty.