The application of resistive random-access memory (RRAM) in storage and neuromorphic computing has attracted widespread attention. Benefitting from the quantum effect, transition metal dichalcogenides (TMD) quantum dots (QDs) exhibit distinctive optical and electronic properties, which make them promising candidates for emerging RRAM. Here, we show a high-performance forming-free flexible RRAM based on high-quality tin disulfide (SnS) QDs prepared by a facile liquid phase method. The RRAM device demonstrates high flexibility with a large on/off ratio of ∼10 and a long retention time of over 3 × 10 s. The excellent switching behavior of the memristor is elucidated by a charge trapping/de-trapping mechanism where the SnS QDs act as charge trapping centers. This study is of significance for the understanding and development of TMD QD-based flexible memristors.