The present invention provides a novel category of naphthalene-based two-photon fluorescent probes having a general formula I, wherein: X is selected from the X1, X2, X3 and X4; The mentioned two-photon fluorescent probes have a low fluorescence background in the non-tumor cells and tissues, and have a strong and specific fluorescent signal in the tumor cells and tissues. These probes have a certain level of water-solubility, while having good membrane permeability. In addition, they have a bigger effective two-photon absorption cross section. The compounds of the present invention also have a lower biotoxicity, phototoxicity and photobleaching. There is sufficient difference between the spectral range thereof and that of a biological sample.