The invention discloses an efficient water treatment device and a water treatment method. The efficient water treatment device is composed of an immersible pump, an original water pool, a pipeline mixer, a sludge pool, a stirring machine, a dense medium coagulation reaction pool, an empty pipe, a PAC (Poly Aluminium Chloride) dosing pump, a PAC storage tank, a dense medium recovery system, a PAM (Polyacrylamide) dosing pump, a PAM storage tank, a sludge pump, a sludge pipe, a disinfectant and chemical cleaning agent dosing device, a rapid settling pool, a water producing or chemical cleaning pipeline, a membrane pool, a disinfectant dosing pipeline, a ultrafiltration membrane module, an aerating system, a cam pump, a water producing or chemical cleaning internal-circulating pipeline, a clean water pool and a sewage draining pipeline. Original water enters the dense medium coagulation reaction pool and then enters the rapid settling pool, excess sludge in the bottom of the settling pool enters the dense medium recovery system, and recovered dense medium reenters a reactor to form circulation. Drained water of the rapid settling pool enters the membrane pool to be filtered and then enters the clean water pool to be disinfected. The efficient water treatment device has the characteristics of saving the used land area and civil engineering cost, good quality of drained water, stable and efficient operation and good economical efficiency, and the dense medium can be recycled.