Abstract: A multi-signal fluorescent probe, represented by: A method for preparing the multi-signal fluorescent probe includes: (a) adding 2-methoxyphenothiazine and ethyl iodide into a mixture of dichloromethane (DCM) and acetonitrile followed by a first reaction and a first post-treatment to obtain 10-ethyl-2-methoxy-10H-phenothiazine; (b) adding boron tribromide into the 10-ethyl-2-methoxy-10H-phenothiazine under an inert gas followed by a second reaction under an ice bath and a second post-treatment to obtain 10-ethyl-10H-phenothiazin-2-ol; and (c) mixing the 10-ethyl-10H-phenothiazin-2-ol, malonic acid, zinc chloride and phosphorus oxychloride followed by a third reaction and a third post-treatment to obtain the multi-signal fluorescent probe. A use of the multi-signal fluorescent probe in the detection of intracellular ONOO? and Na2S2 is also provided.