The invention provides a RSA modular exponentiation calculation method and device. The RSA modular exponentiation calculation method comprises the following steps: acquiring information m, a modular number N, a random number r, a public key e and a private key d; calculating a first value m0, wherein the first value m0 is a value that N is delivered from the product of re-1 and the information m; calculating a second value m1, the second value m1 is a value that N is delivered from the product of the first value m0 and the random number r; calculating a third value S1, the third value S1 is a value that N is delivered from (m1)d-1; acquiring RSA encryption result S corresponding to information m, and the result S is the result that N is delivered from the product of the third value S1 and the first value m0. By adopting the method and the device, base number randomization on RSA can be achieved through relatively small expense, so that power consumption analysis attack can be avoided.