The invention discloses a modular multiplication operator implemented by a series-parallel combination way, and belongs to the field of elliptic curve cryptography algorithms. The binary field bit-width-variable modular multiplication operator comprises a partial product multiplication unit, a word level multiplication unit, an output cache unit, a data shifting unit and a control unit. The modular multiplication operator is based on a polynomial basis under a binary field; input data are read in an MSB-first (Most Significant Bit first) way; the step number of loop computing is controlled according to computing digits by a state machine; a word multiplication operation and a partial multiplication operation are performed concurrently in the steps; and lastly, computing results in all the steps are integrated, and output in series. The operating rate is increased in the series-parallel combination way, and the computing complexity is lowered. Meanwhile, a bit multiplier capable of computing data of a plurality of bit widths is designed internally, so that reutilization of a hardware structure is realized. Compared with the prior art, the modular multiplication operator is more advantageous on the aspects of area, flexibility and the like, and a relatively high operation rate is ensured at the same time.