Abstract: To solve the problem of long cycle of calculation modular division with traditional way, in this paper, an improved Montgomery modular division algorithm is proposed based on the original Montgomery modular inversion algorithm. The algorithm compared calculation with modular inversion-division way can reduce 34% cycle. A modular division device is designed to operate in both finite fields GF(p) and GF(2ⁿ) based on the proposed algorithm. We synthesize the modular division device under 0.18 μm CMOS technology and the clock frequency can reach 270 MHz. Compared with original Montgomery division, the design can support the calculation below 576 bits and can reduce 15% cycle calculating modular division. Comparing with modular inversion-division way, 45% speed of modular division faster can be accelerated.