The invention relates to a determining method for principle parameters of a DC-based deicer, which comprises the following steps: 1) collecting principle parameters of each circuit in application scope of a DC-based deicer, 2) operating and determining the minimum deicing current according to historical weather conditions, taking the maximum value in the minimum deicing current of each circuit as a rated current of the DC-based de-icer, 3) utilizing the minimum deicing current and a deicing way to calculate direct current voltage and capacity of the DC-based deicer, 4) utilizing 1.2 times of the minimum deicing current and a deicing type to calculate output voltage and capacity of the DC-based deicer, 5) taking the maximum value of the direct current voltage and the maximum value of the capacity calculated in the step 3) and the step 4) as the rated direct current voltage and rated capacity of the DC-based deicer, and 6) defining the overload capacity of current and capacity of the DC-based deicer as 1.2 times of rated two hours. The invention can optimize each parameter of the DC-based deicer, can reduce capacity of the DC-based deicer as much as possible on the premise of guaranteeing each circuit of the DC-based deicer to deice fast to further reduce investment in the DC-based deicer. The invention can be applied to the designs of DC-based deicers in each transformer substation in an electrical power system, and has good application prospect.