Not only considering the fuzziness of structuralphysical parameters and geometric dimensions, but also considering fuzzinessof applied load simultaneously, fuzziness of structural dynamic response isstudied in this paper. Firstly, a new method (fuzzy factor method) to dealwith fuzzy variable is proposed. By means of this new method, a fuzzyvariable can be described as its fuzzy main value multiplied by its fuzzyfactor. Secondly, from Duhamel integral, the expressions of structural fuzzydynamic response are deduced by combining mode superposition method withcalculus, fuzzy factor method and interval arithmetic, and membershipfunctions of dynamic response can be derived in the end. To testify thecorrectness and rationality of the model and solution to it given in thispaper, Monte Carlo method is used to simulate the fuzzy structure in theexample. At last, through engineering example, the influences of the fuzzystructural parameters and fuzzy applied load on structural fuzzy dynamicresponse are inspected and some significant conclusions are obtained.