The present invention discloses a plasmon enhancement based electron emitting device and method with light enhancement/modulation. The device includes: a package structure, a power source and a light source, wherein the package structure has a cathode and an anode; a through hole is formed in the anode, the cathode is disposed on a conductive substrate, and the cathode is a field-emission cathode constituted by a cathode substrate and metal nanostructures attached to a surface of the cathode substrate; the power source forms an electric field between the cathode and the anode; and the light source emits laser light incident on the metal nanostructures of the cathode through the through hole of the anode. In the light enhancement/modulation electron emission device of the present invention, the incident light emitted by the light source causes enhancement of the electron emission of the field-emission cathode which is formed by combination of field-emission material of the cathode substrate and the metal nanostructures, so that the electron emission efficiency is increased. Meanwhile, by changing the intensity, wavelength and polarization of the incident laser, a local field of the surface of the field-emission material is adjusted, and light modulating electron emission is achieved.