The invention discloses a protoperidinuim culture medium and method. The protoperidinuim culture medium is composed of, by weight, 20-100 mg of NH4NO3, 20-60 mg of CO(NH2)2, 1-10 mg of KH2PO4, 100-800 mg of NaHCO3, 15-50 g of MnCl2 4H2O, 10-30 mg of FeC6H5O7 5H2O, 1*10-5-1*10-3 mg of VB12, 50-200 mg of VB1, 0.5-5 mg of KCl, 10-15 mg of Na2EDTA, 0.2-5 g of chitosan oligosaccharide with a molecular weight of 1500-2000 Da, and 1000 mL of seawater. The protoperidinuim culture method comprises the steps of phase one, conical flask culture and phase two, mineral water barrel culture. The protoperidinuim culture medium and method provides the optimal nutritive salt formula for protoperidinuim culture, thereby improving the yield of protoperidinuim poison and reducing the culture cost; compared with traditional outdoor open cement ponds expanded culture manners, culturing protoperidinuim in mineral water barrels is lower in cost, less prone to pollution and easier to operate and can greatly reduce workload, increase the growth speed of the protoperidinuim and shorten the culture period.