The invention provides a shrimp-crab mariculture system and a shrimp-crab mariculture method, which belong to the field of aquaculture techniques and are used to solve the technical problem that existing shrimp-crab mariculture systems are low in cultivation efficiency, low in intensive degree and the like. The shrimp-crab mariculture system comprises a seawater purification device, a seawater heating device, a sewage treatment device, a culture pond, a temporary culture pond and a crab breeding device. The shrimp-crab mariculture method includes steps: A, purifying seawater, and heating the purified seawater; B, delivering the heated seawater to the temporary culture pond, the culture pond and culture boxes; C, transferring shrimp seeds to the culture pond, breeding the shrimp seeds into adult shrimps, and breeding crab seeds into adult crabs; D, catching the adult shrimps, disinfecting rich water to breed other shrimps, and catching the adult crabs to breed other crabs. The shrimp-crab mariculture system and the shrimp-crab mariculture method have the advantages of high breeding efficiency, high intensive degree, high survival rate and the like.