The invention discloses a launching performance evaluation device and an evaluation method for an electron beam of a field emission electron source. The evaluation device comprises a vacuum cavity, a vacuum pumping system, a vacuum degree measurement system, an electronic gun assembly, a power supply system, an electron beam imaging system, an electron beam deflection system and a detection and acquisition system. In the evaluation device, two deflection magnetic fields in a perpendicular direction are installed on a path of the electron beam and used for controlling the electron beam to sequentially scan and pass through a small hole on a fluorescent screen from edge to center so as to obtain important launching performance quantitative parameters such as electron beam spot shape, the beam intensity of a center beam of the electron beam spot, beam density, angle current density and electron beam launching stability of the field emission electron source, and after the above quantitative parameters emitted from the electron of the electron source are obtained, a quantitative basis is provided for evaluation on the performance of the field emission electron source, optimization on the preparation process of the field emission electron source and improvement on the preparation platform of the field emission electron source.