Abstract: An area-first design method for multifunctional and reconfigurable large number calculators was brought forward. Based on the addition algorithm, the design was optimized by the method of scan chain control and iterative invoke and realized 14 kinds of large-number operations such as addition, subtraction, multiplication, division, module addition, module multiplication, module exponential, etc. Every operation supported the data length from 8 bits to 2 048 bits, which afforded security chip users' maneuverability, and reduced the time and cost of coding remarkably. Under the speed restriction of architecture, operations reused the same logic units as possible and the design just contained 13 887 gats, which could meet the requirement of area-first design completely.