Metal-organic frameworks (MOFs) are often acted as potential candidates for the construction of efficient nanozymes due to their unique metal-ligand assembly structure, which can mimic different enzyme activities by modulating the metal nodes and ligand environment. In this study, a three-in-one composite metal-organic framework nanozymes (CeCu-MOFs) with excellent intrinsic peroxidase-like, oxidase-like, and catalase-like catalytic properties have been successfully prepared in environmentally friendly manner by a one-step chemical deposition method. Meanwhile, a catalytic platform for signal amplification was designed for quantitative measurement of ascorbic acid (AA) using the oxidase-like characteristic of CeCu-MOFs. The constructed colorimetric sensor achieved selective identification and accurate measurement of AA, demonstrated good linearity in the range 0.1-50 μM with a detection limit of 0.063 μM. We, further developed a portable smartphone-based platform for visual colorimetric determination of AA in real samples in point-of-care (POC) fashion by utilizing a portable paper-based device.