Observation of charge coupling effect is important to characterize the electrical behaviors of triple-junction solar cells (TJSCs). Electric modulus (M) spectroscopy incorporated with adequate lasers is demonstrated to be an effective approach to investigate the internal electrical characteristics of the individual subcells in InGaP/InGaAs/Ge TJSCs. The distinct characteristic peaks of imaginary part of M corresponding to three individual subcells are identified, as specific lasers are applied. The charge coupling between the excited subcell and neighboring subcell is observed, which causes the expansion of the depletion region in the latter. This approach provides the information of charge coupling for the design of TJSCs.