The structural vibration fatigue test usually takes a long time under actual load excitation, so the accelerated test method is often used instead. The key to accelerated test design lies in establishing the mutual relationships between the different excitation spectrum, response stress and fatigue life. Fatigue life analysis in the frequency domain has the significant advantages of simple calculations, low computational complexity and good engineering practicability. Frequency-domain analysis in particular was the only method that solves the problems of fatigue loading with dynamic characteristics. Based on the Bendat and Dirlik methods and through theoretical derivation, this paper approves and establishes the linear relationships between the three and proposes a new way to determine the excitation spectrum magnitude used in the accelerated test based on the above linear relationships and finite element simulation results. A simulation verifies the feasibility of the proposed method.