The invention discloses a porous carbon nanosheet material, a preparation method thereof and application of the porous carbon nanosheet material serving as the negative electrode material of sodium-ion batteries. The preparation method includes: placing dopamine into a lithium chloride solution to perform polymerization reaction to obtain polydopamine-lithium chloride gel; subjecting the polydopamine-lithium chloride gel to high-temperature carbonization treatment to obtain a porous carbon nanosheet precursor; subjecting the porous carbon nanosheet precursor to argon plasma etching to obtain the porous carbon nanosheet material. The preparation method has the advantages that the method is simple, easy in raw material obtaining, good in repeatability and capable of achieving industrial production; the prepared porous carbon nanosheet material is large in specific surface area, rich in reaction active sites, moderate in interlayer spacing and the like; the porous carbon nanosheet material shows good battery performance hen being applied to the sodium-ion batteries.