The invention particularly relates to a negative-sequence-current-based control method of conversion chain average direct voltage. The method comprises the following steps: comparing the average direct voltage of any two phases of three phases of conversion chain with the average value of direct current of all chain nodes to obtain average direct voltage deviation of the two phases of conversion chain, and processing by a PI (Proportional Integral) controller to obtain the active power deviation of the corresponding phase of conversion chain; combining the active power deviation and the effective value of alternating current side system voltage to obtain the negative-sequence current component instruction of the three phases of conversion chain through the negative-sequence current instruction calculation; transforming the of three-phase negative-sequence current component instruction into dq axis component of negative-sequence current instruction through Park Transform; obtaining the dq axis component of negative-sequence modulation wave voltage through negative-sequence current decoupling control; then carrying out inverse Park Transformation to obtain the reference value of the three-phase negative-sequence modulation wave voltage; and controlling the output of a converter to form a closed-loop control. The method can effectively solve the problem of conversion chain average direct voltage unbalance and has the characteristics of excellent control performance and wide application range.