The inverse sub-structuring method by using the easily measured system-level FRFs to predict the substructure-level FRFs and the dynamic stiffness of coupling interface. In most engineering application practices, the system-level FRFs from coupling degree of freedoms may not be measured accurately because of there might be some fragile structure in the coupling interface and the difficulties of vibration excitation and response measurement for the coupled interface between components within the limited accessible space. In this paper, the aim is to develop a new FRF-based indirect inverse sub-structuring method for the analysis of the dynamic characteristics of a three-component coupled mechanical system without measuring system-level FRFs at the coupling degree of freedoms. Using a frequency response probe to predict the unmeasured interface auto FRF, the theoretical derivation of the theoretical formula of the frequency response probes is given firstly, then the technology is verified by a finite element simulation, showing exact agreement. The new method shows its great application prospect for obtaining unmeasured data from the coupling interface.