The invention discloses a control method for reducing a running risk of a hybrid doubly-fed DC system under a power grid fault. The control method comprises the steps of setting a first control target, a second control target and a third control target, and calculating power running ranges Omega1, Omega2 and Omega3 corresponding to the control targets; showing the power running ranges Omega1, Omega2 and Omega3 in a PQ planar coordinate system to obtain different types of safety domains conforming to different control targets, calculating a passive power running point Q<*> of a voltage source converter based high voltage direct current (VSC-HVDC) inversion station under the power grid fault according to the types of the safety domains, calculating an inner ring current control instruction according to the passive power running point Q<*>, and outputting the inner ring current control instruction by the VSC-HVDC inversion station so as to achieve control on the running risk ofthe hybrid doubly-fed DC system under the power grid fault. The whole safe running of the hybrid doubly-fed DC system under the power grid fault is ensured by considering prevention of commutation failure of a line commutated converter high voltage direct current (LCC-HVDC) conversion station under the power grid fault of a receiving end, safety of the VSC-HVDC inversion station and safety constraint of a power frequency of a sending end.