This invention discloses a method and a system to achieve an integration of in-situ dewatering and consolidation of fluid tailings, and treatment of tailings water in tailings pond. The said method comprises multi-steps, including: a) installing floating working platforms for installation of treatment units of the treatment system, b) using gas flotation unit for bitumen removal and pH adjustment in fluid tailings, c) using submerged filtration unit for in-situ dewatering and consolidation of fluid tailings, in-situ deposition of consolidated tailings to the bottom of tailings pond, and in-situ recovery of tailings water, d) using in-situ flocculation and thickening unit for ultrafine tailings treatment and in-situ deposition, and e) using water treatment unit for tailings water treatment and in-situ waste disposal. The in-situ integration of the treatment units provides a cost-effective process to speed up tailings pond reclamation and water recovery from tailings pond.