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