The invention discloses a control method for low frequency after large-scale draught fan tripping. The control method comprises the following steps: step one, monitoring direct current operation active power information Pdc of a wind power collected ultra-high-voltage direct current send-out type power grid, wind power online active power capacity information Pw and frequency information f and fault information of important nodes, when the fault that the frequency of the power grid is decreased caused by draught fan tripping occurs, transferring to step two; step two, if the wind power onlineactive power capacity information loss delta Pw is greater than a set threshold value Pset_mk and f is lower than a set threshold value fset_mk after t1 seconds are delayed, delaying t2 seconds to start emergency direct current power support, and transferring to step three; and step three, determining the direct current of the active power emergency support, active power emergency support direction and active power emergency support controlled total target value P total_dc, and distributing the P total_dc to each direct current for implementation. The frequency chain reaction caused by draughtfan tripping is effectively blocked.