A new imine-linked covalent organic framework (COFDHA-TAPB) with strong fluorescence is designed by using 2,5-dihydroxybenzaldehyde (DHA) and 1,3,5-tri(4-aminophenyl)benzene (TAPB) as monomers. The TAPB has a suitable aromatic skeleton in which slight distortion between phenyl groups reduces aggregation-caused quenching (ACQ). The hydroxyl group side chains of DHA form hydrogen bond with the imine bonds of COFDHA-TAPB to restrict intramolecular rotations. Hydrogen bonds are also formed between different layers of COFDHA-TAPB, which further restricts supramolecular rotation by narrowing the layer spacing. Moreover, the COFDHA-TAPB exhibits a hollow sphere structure, which also reduces ACQ and intramolecular rotation. Therefore, COFDHA-TAPB has a strong emission peak at 408 nm, which is used for nitrofurazone detection. The detection linear range is 0.33 µm–0.197 mm (0.066–39 µg mL−1), and the detection limit is 0.11 µm (0.022 µg mL−1). This work also provides an important guideline to design strongly fluorescent covalent organic framework by controlling layer spacing, aromatic linkers sizes and side chains of monomers for sensors.