Abstract: Based on the limited resources of tiny terminals lead to the problem of single encryption algorithm, the S-box as the key components of the block cipher is reconfigurable designed. This paper put forward an 8-1 S box as the basic reconfigurable unit, converts S box of Boolean function expressions, with the method of grouping variable, and recursive calculation, dramatically reduced expression of and-item number, increase the utilization of intermediate results. On this basis, we design a reconfigurable unit S box, and under the TSMC 45 nm CMOS technology synthetically. The working frequency can reach 1.67 Ghz, compared with the existing research results, this design can well satisfy the current demand of the speed of the microprocessor. At the same time, the resource usage is only two-thirds of similar design.