As a key chemical raw material, hydrazine hydrate (N2H4) is widely used in chemical manufacturing, aerospace propulsion and pharmaceuticals synthesis. However, excessive N2H4 causes serious harms to the environment and organisms. Herein, a ratiometric fluorescence probe CDP has been designed and synthesized from p-hydroxycinnamic acid. Upon interaction with N2H4, the major fluorescence emission peak at 570 nm is blue-shifted to 455 nm, accompanied by a fluorescence color change from pale orange to blue. The detection limit of CDP for N2H4 is determined as 17.08 nM. Experimental data further indicate that probe CDP can effectively detect N2H4 across a broad pH range (5-12). More notably, probe CDP demonstrates significant potential for imaging N2H4 in living cells and mice models. Moreover, probe CDP can be employed for the detection of N2H4 in soil samples and water samples. This work describes a versatile fluorescence probe for detecting N2H4, underscoring its considerable potential in environmental analysis and public health monitoring.