Abstract: This paper presents the design of a field emission carbon nanotube cold cathode micro-focus electron gun. The cathode is shaped as a cone divided symmetrically into two, with the cut surface serving as the base, and is evenly distributed in a cylindrical groove to form a circular array. This design features a concave shape with a pre-focusing effect, providing more optimal incident conditions for the subsequent focusing system. In addition, the design includes a rhombic grid mesh and a hyperbolic focusing electrode. The cathode employs a micro-tip design, significantly enhancing the electric field intensity at the tip, which improves the emission current density and reduces the turn-on voltage; the rhombic grid mesh enables a high electron transmission efficiency, and the hyperbolic focusing electrode optimizes the electric field distribution to achieve efficient focusing of the electron beam, ultimately resulting in a beam compression ratio of 955. The field emission performance of the electron gun was analyzed using CST finite element electromagnetic simulation software. Through optimizing the geometric parameters and adjusting the voltage distribution, the electron gun achieved an electron transmission efficiency of 92.4%, an anode current of 279.1 μA, and a focal spot size of 12 μm at an anode voltage of 120 kV.