The 3D supramolecular framework (3D‐SF) is constructed in this work through the hydrogen bond assisted self‐assembly of spherical dendritic nanopolymer to regulate the flexibility, stability, and resistive switching (RS) performance of perovskite resistive random‐access memory (RRAM). Herein, the 3D‐SF network acts as the perovskite crystallization template to regulate the perovskite crystallization process due to its coordination interaction of functional groups with the perovskite grains, presenting the uniform, pinhole‐free, and compact perovskite morphology for stable flexible RRAM. The 3D‐SF network in situ stays at the perovskite intergranular boundaries to crosslink the perovskite grains. The RS performance of 3D‐SF‐modified perovskite RRAM device is evidently improved to the ON/OFF ratio of 105, the cycle number of 500 times, and the data retention time of 104 s. The 50‐days exposure of unencapsulated RRAM device at ambient environment still makes the ON/OFF ratio to be kept at ≈104, indicating the potential of long‐term stable multilevel storage in the high‐density data storage. The bending action under different radius also does not change the RS performance due to the excellent bending‐resistant ability of 3D‐SF‐modified perovskite film. This work explores a novel polymer additive strategy to construct the 3D supramolecular framework for stable flexible perovskite optoelectronic devices.