The invention discloses a tidal mixed flow constructed wetland system and a sewage treatment method thereof. The constructed wetland system comprises wetland pools and a circulating filtration system, wherein each wetland pool comprises a filler bed body, microorganisms in the filler bed body and aquatic plants above the filler bed body, the filler bed body comprises an underflow biological contact layer and substrate layers above the underflow biological contact layer, and a separation net is arranged between the underflow biological contact layer and the substrate layers; the circulating filtration system comprises a circulating filter pump, a water inlet pipe, a water outlet pipe and an electromagnetic control device. Anaerobic and aerobic processes of sewage treatment are performed alternately in the first pool and the second pool through the filter pumps, tidal flow is formed, when water circulates in the circulating system, the substrate layer 3 filers sewage particles, the sewage particles are aggregated, the particles are adsorbed by biological films to form particle blocks, the blocks and large particles formed by phosphorus-accumulating bacteria and the like are discharged after filtered by the filtration system, meanwhile, pollutants decomposed into soluble components are removed through the biological films and root systems of the aquatic plants, and a good nitrogen and phosphorus removal effect is realized.