Abstract: A pH fluorescent probe capable of detecting both acidic and alkaline ranges was designed and synthesized from pyrene-1-carboxaldehyde and 3, 4-dihydroxybenzaldehyde. The spectroscopic experiment results show that in dimethyl sulfoxide (volume fraction being 30%) aqueous solution, the probe has colorimetric and fluorescence responses for detecting pH in both pH < 6.0 and pH>9.5, the pK_a values being 4.69 and 10.40, respectively, while there is almost no similar recognition of other ions under the same conditions. Therefore, the probe has a specific recognition response for pH detection in the acidic and alkaline ranges.