This paper presents the analyzed results on small-signal stability of a grid-connected tidal power-generation system (GCTPGS) as affected by system-parameter variations. The studied GCTPGS containing a permanent-magnet synchronous generator driven by a tidal turbine through a gearbox is connected to a power grid through power-electronics converters, a submarine cable, and a step-up transformer. A d-q axis equivalent-circuit model and the associated linearized system equations are derived to establish the complete small-signal model of the studied GCTPGS. A frequency-domain approach based on eigenvalue techniques and a time-domain scheme based on nonlinear-model simulations are both carried out to systematically determine the characteristics of small-signal stability of the studied GCTPGS under different operating conditions. It can be concluded from the simulation results that the studied GCTPGS subject to the variations of different system parameters and under operating conditions can maintain small-signal stability.