The invention discloses a control method and a control device of a fan converter. The method comprises the steps of taking a larger value in a power grid line voltage peak value and a stator line voltage peak value as an initial given value Vdc_given0 of direct current bus voltage; inputting a larger value in modulation degrees of a grid side converter and a machine side converter as feedback quantity and a target modulation degree of the grid side converter as given quantity to a modulation degree closed loop regulator of the grid side converter, wherein output quantity delta U of the regulator is a given compensation value delta Vdc_given of the direct current bus voltage, and a given value Vdc_given of the direct current bus voltage is equal to Vdc_given0 plus delta Vdc_given; storing delta U in a register and then switching delta U into a given compensation value with a symbol as shown in the specification of positive-sequence sensitive reactive current when Vdc_given is greater than rated voltage Vdc_ed of a direct current support capacitor; taking 0 as an initial value of delta U; and switching delta U into delta Vdc_given and taking delta Vdc_given stored in the register asthe initial value of delta U when Vdc_given is detected as less than or equal to Vdc_ed. According to the control method and the control device, the converter can self-adaptively operate at the optimal direct current bus voltage.