NOVELTY - Preparing polyhydroxyalkanoate by quick aerobic activated sludge mixed flora acclimatization comprises taking activated sludge into a sequencing batch reactor, aerating, controlling the dissolved oxygen content, precipitating, discharging, passing water for second time, aerating, precipitating, discharging water, where the first time fed water contain carbon, nitrogen and phosphorus sources and second time fed water contains only nitrogen source, transferring discharged sludge water mixed solution into the reactor, allowing to stand, adding carbon source into the supernatant and aerating.    USE - The method is useful for preparing polyhydroxyalkanoate by quick aerobic activated sludge mixed flora acclimatization (claimed).    DETAILED DESCRIPTION - Preparing polyhydroxyalkanoate by quick aerobic activated sludge mixed flora acclimatization comprises taking activated sludge with high diameter ratio of 10:1 into a sequencing batch reactor (SBR) until the sludge concentration reaches 3000-5000 mg/l, (b) processing for 6-12 hours in the reactor, opening a first inlet, firstly passing water, controlling the temperature of the SBR reactor to be 20-25 degrees C, aerating, controlling the dissolved oxygen content to be 2-3 mg/l, stopping the aeration when the content is increased to 6-7 mg/l, precipitating for 3-5 minutes, discharging water, opening a second water inlet, aerating for 5-11 hours, precipitating for 30 minutes, discharging water, where the first time fed water contain carbon source, nitrogen source and phosphorus source with carbon, nitrogen and phosphorus elemental ratio of (110-90):(7-5):1 and has a chemical oxygen demand (COD) of 1000-5000 mg/l, and the second time fed water contains only nitrogen source and not carbon and phosphorus sources, where the carbon source is a small organic molecule, and the water ratio is 1:1, and (c) carrying out the operation for 2-4 days, where the sludge retention time in the SBR reactor is 1-10 days, and collecting the discharge of the sludge water mixed solution each day, (d) transferring the sludge water mixed solution into the reactor to remove supernatant to half the volume, allowing to stand, collecting the precipitate, adding equal volume of carbon source into the supernatant, aerating until dissolve oxygen content in the reactor is 2-3 mg/l, stopping the aeration when the content is 6-7 mg/l, and (e) repeating the step (d) for 6-8 times.