Communicated by Q. ChenThis paper is concerned with a generalized Arzela-Ascoli's lemma, which has been extensively applied in almost periodic problems by the continuation theorem of degree theory. We give a counter example to show that this lemma is incorrect, and there is a gap in the proof of some existing literature, where the addressed generalized Arzela-Ascoli's lemma was used. Moreover, we make some final comments and introduce an open problem.