The invention relates to an electrostatic ion trap having a central axis and a central symmetrical plane perpendicular to the central axis. The electrostatic ion trap comprises an inner electrode group arranged along the central axis and a pair of outer electrode groups arranged on two sides of the central symmetry plane along the central axis. Each outer electrode group comprises a plurality of electrode plates. The plurality of electrode plates are circumferentially distributed around a periphery of the inner electrode group and centered on the central axis. At least two electrode plates in the same outer electrode group are electrically connected. A potential difference is formed when voltages are respectively applied to the inner electrode group and the outer electrode groups, thereby forming a space for trapping ions between the inner electrode group and the outer electrode groups.