The retrofit of helicopter is an important content in the development of helicopter. How to quickly and efficiently carry out the structural changes in the fuselage meeting the requirements of the dynamic properties of the fuselage is a technology with important engineering value. In the paper, the first six modal frequencies and mode shapes of Z11 helicopter fuselage are calculated by using the finite element model of the helicopter, and the sensitivities of parameters to the dynamic properties are analyzed. The influences of mass, Young′s modulus and geometric properties on the dynamic properties of helicopter fuselage are investigated. Parameters affecting the dynamic properties most are obtained and their locations are given. The result gives a design guideline for the retrofit of helicopter fuselage.