The invention discloses a control method and system for a permanent magnet direct drive wind power system. The control method is used for controlling the energy output of the permanent magnet direct drive wind power system, and comprises steps of: calculating a reference current by using a virtual synchronous generator algorithm according to a reference active power value and the active power actually fed into a power grid; transforming the reference current into a two-phase synchronous rotating coordinate system to obtain an active current component; obtaining a reference value of the reactive current; obtaining voltage vector d-axis and q-axis components by current control according to the active current reference value and the reactive current reference value; obtaining a three-phase ACvoltage signal; and obtaining a switching signal of a grid-side converter by using sinusoidal pulse width modulation according to the three-phase AC voltage signal. The active current component is calculated by using the virtual synchronous generator algorithm and then is transformed, thus, the current simulates the inertia of the synchronous generator and reduces the fluctuation of the energy fed into the power grid by the wind power system.