The drift tube assembly provides the axial trap for ions in an electron beam ion trap(EBIT). It works under low temperature

strong magnetic field

ultra high vacuum and high electric potential

which leads to high requirements for its design. In this paper

the design of the potential trap

the structure of the assembly

the procedures for solving engineering problems

and the tests about low-temperature and high-voltage operation of the assembly are introduced. This work plays an important role in the development of the Shanghai EBIT

which can be operated stably at present with an electron beam of 100kV/110mA.