Abstract: In allusion to the subsynchronous oscillation in power grid, the open-loop modal resonance analysis method was used to research the multi open-loop modal resonance caused by the grid-connection of multiple parallel permanent magnet synchronous generators (abbr. PMSG) possessing same parameters, and a closed-loop interconnection model composed of the PMSGs regarded as feedback subsystem and the rest part of the power grid regarded as feedforward subsystem was constructed. In allusion to the oscillation modes dynamically dominated by outer-loop of DC voltage control of grid-side converter and phase-locked loop (abbr. PLL), the multi open-loop modal resonance between the two subsystems was researched. Results of modal analysis and calculation show that the grid-connection of multi PMSGs will lead to the reduction of damping of PLL mode, and the increase of the number of grid-connected parallel PMSGs will lead to subsynchronous oscillation in power grid.