The invention discloses a technique for treating pig raising liquid waste by a circular anaerobic reactor, a sequencing batch biofilm, a constructed wetland and a facultative lagoon, which comprises the steps: pig farm liquid waste automatically flows into a collection pipe network through a pipe tunnel and flows through a grating and a hydrolysis acidification pool to remove the large granular pollutants and floaters in the liquid waste so as to improve the biodegradability of the liquid waste; the liquid waste enters external and internal circular anaerobic reactors to remove most part of COD by the efficient anaerobic digestion function, and the liquid waste enters a successive regulating pool; the water flowing out from the regulating pool enters a sequencing batch biofilm reactor, and the water is supplied with air by a blower to perform nitration reaction at the aeration stage and to perform anoxic / anaerobic nitration reaction at the stationary stage so as to further remove the pollutants in the liquid waste, such as COD, ammonia nitrogen and phosphorus, and the like; the water discharged from the sequencing batch biofilm reactor flows into a constructed wetland to better remove pollutants in the liquid waste, such as COD, N and P, and the like; the water discharged from the constructed wetland flows into a facultative lagoon for further denitrogenation and dephosphorization treatments, and the water is discharged after satisfying a discharge standard.