Abstract: Analyzing the switching process of Keil C51 in BANK compile mode, this paper proposes a method using a BANK switching technique to solve the problem that only 64K bytes of code space can be accessed in a single-chip computer. On the basis of this analysis this paper presents and validates a design method on software and hardware, thus solving the problem that the typic 8051 only provides 16 address lines for addressing code space in spacecraft equipments.