The invention discloses a structured mixed bit-width multiplying method and a structured mixed bit-width multiplying device. The method includes the steps: 1) inputting a multiplier, a multiplicand and a computing control signal; 2) splitting the multiplier and the multiplicand and performing sign bit expansion for the multiplier and the multiplicand; 3) importing the multiplier and the multiplicand to two MXN multiplying units for Booth decoding and generating partial products, and compressing the partial products; 4) generating a corrected value; and 5) compressing a compressed output result and the corrected value to obtain a multiplying result. The device comprises an operand selection and expansion unit, the first MXN multiplying unit, the second MXN multiplying unit, a correcting unit and a final product arithmetic element, wherein the operand selection and expansion unit is connected with the final product arithmetic element through the MXN multiplying unit, the second MXN multiplying unit and the correcting unit. The structured mixed bit-width multiplying device has the advantages of high hardware use ratio and area use ratio, high arithmetic speed, low hardware expenditure, simple structure and orderliness in obtained territory.