In this paper, we extend the classical Weyl's lemma to RCD(K, N) metric measure spaces. As its applications, we show the local regularity of solutions for Poisson equations and a Liouville-type result for L 1 very weak harmonic functions on RCD(K, N) spaces. Meanwhile, as an application of regularity theory on non-smooth settings, we obtain a gradient estimate for solutions to a class of elliptic equations with discontinuous coefficients.