The invention discloses a positive plate of a lead storage battery and a preparation method thereof, and belongs to the technical field of lead storage batteries. A lead paste raw material of the positive plate comprises lead powder, an additive, water and sulfuric acid; the additive comprises diantimony trioxide and stannous sulfate; the preparation of lead paste is completed in two parts: in the first part, the additive contains the diantimony trioxide and the stannous sulfate, the reaction temperature is controlled not to be greater than 50 DEG C, and first lead paste containing 3BS is prepared; in the second part, the two additives are not contained, the reaction temperature is controlled to be 80-85 DEG C, and second lead paste containing 4BS is prepared; the first lead paste and the second lead paste are physically mixed, so that an effective amount of 3BS and 4BS is simultaneously contained in the positive lead paste; meanwhile, the battery performance in terms of initial capacity and battery life is improved. The positive plate disclosed by the invention has the benefits that a medium temperature lead paste mixing and curing process is adopted, the conversion of the 4BS and the further particle size increase are avoided, the particle size and the content of the 4BS in the lead paste are effectively controlled, and the battery consistency is ensured.