A microarrayed Einzel lens (MAEL) is adopted in many high throughput applications, such as multibeam lithography, multibeam electron microscope, and multibeam electron beam inspection. The assembly and fabrication errors of mounting an MAEL consist of misalignment, tilt, and ellipticity, which strongly affect the property of the MAEL. In this report, the accuracy requirements of mounting an MAEL are analyzed using Munro’s electron beam software. The results show that the assembly errors of the middle electrode in an MAEL are dominant in spoiling the beam quality. When assembling an MAEL, for a probe size of 10 nm, the requirements on misalignment, tilt, and ellipticity are 2.7 μm, 1 mrad, and 60 nm, respectively, while for a probe size of 1 nm, the assembly accuracy should be controlled to be less than 0.8 μm, 0.7 mrad, and 6 nm, respectively. These calculated results could be able to instruct designing an MAEL. Moreover, a dedicated tool is necessary for assembling the MAEL to ensure that the accuracy requirements of the MAEL are acceptable, to make good quality electron probes.