The invention discloses a multi-direct current power transmission output power system stable state frequency control method. The multi-direct current power transmission output power system stable state frequency control method comprises steps that S1, various related parameters are acquired; S2, a bus admittance matrix of a sending end power grid and a bus admittance matrix of a receiving end power grid are formed based on the acquired parameters; S3, related information before occurrence of disturbances is acquired; S4, related information after the occurrence of the disturbances is acquired; S5, the equality constraint condition of the multi-direct current power transmission output power system stable state frequency control method is established; S6, the inequality constraint condition of the multi-direct current power transmission output power system stable state frequency control method is established; S7, the minimization objective function of the multi-direct current power transmission output power system stable state frequency control method is established;S8, the optimization result of the multi-direct current power transmission output power system stable state frequency control method is acquired, and technical effect of optimization coordination control of multiple direct currents is realized.