This article presents a complex-valued phasor domain admittance modeling technique for the equivalent circuit modeling and dynamic stability analysis of a single-phase grid-tied voltage-source converters system considering infinite-order frequency-coupling (IOFC). The basis is the symmetric structure of admittance model in rotating phasor domain, whose complex-valued admittance component can capture the frequency coupling effect. Thereafter, the equivalent circuit model (ECM) considering IOFC is established by analyzing the mechanism of coupling phenomena in detail. The proposed ECM model provides an insightful physical recognition to illustrate IOFC effect. Besides, the model is single-input and single-output (SISO), which facilitates measurement and analysis. It is found that high-order coupled frequency components are produced by low-order coupled frequency components, and its impact declines with the increase of order, which provides instruction for model order truncation. Further on, the influences of grid stiffness, phase-locked-loop bandwidth, and reference current are analyzed. These results show that the system is more likely to be unstable and the frequency coupling phenomenon is easier to be observed when the system is under weaker grid stiffness, wider PLL bandwidth, or larger reference current. Finally, experiments verified the established model and dynamic stability analysis.