Abstract: Aiming at the urgent needs for modulation technique of electronic packet width, we propose a compact symmetric type electron packet width modulation technique. The core of which is the introduction of the carefully chosen alternating electric field, which imposes differential energy modulation on electrons of different part in the electron packet, achieving the purpose of modulating the width of the electron packet. The details are given, including the choosing of the alternating electric field, pulse modulation amplitude relationship and the transverse confinement of the axial magnetic field. The requirements for both compression and broadening modulation in different types of modulating electric field are obtained. The example demonstrates its validity.