NOVELTY - Preparing a new type of polyhydroxyalkanoate (PHA) comprises: (a) cultivating Ralstonia eutropha strain; (b) fermenting in shaking bottle; (c) performing tank fermentation; and (d) measuring PHA content.    USE - The method is useful for preparing a new type of polyhydroxyalkanoate, which can be used as an ideal plastic alternative material (all claimed).    ADVANTAGE - The PHA is a new type of an environment-friendly biological material (claimed). The method not only decreases production cost but also obtains higher dry cell weight and PHA yield through fed-batch fermentation. It provides a good direction for treating organic wastes, which not only solves the problem of treating organic wastes, but is also beneficial to the environment.    DETAILED DESCRIPTION - Preparing a new type of polyhydroxyalkanoate (PHA) comprises: (a) cultivating seeds: inoculating Ralstonia eutropha strain growing well on slant culture medium to a 500 ml triangular bottle filled with 100 ml of seed culture medium, controlling rotor speed of the shaking bottle at 200 revolutions/minute (rpm), temperature is 30 degrees C and culturing time is 30 hours; (b) fermenting in shaking bottle: filling 75 ml of liquid in a 500 ml triangular bottle, controlling inoculating amount as 10%, rotor speed of the shaking bottle is 200 rpm and temperature is 30 degrees C, and fermenting for 36 hours; (c) performing tank fermentation: controlling agitating speed of a 5 L tank at 400 rpm and permeated volume at 4.5 L/minute; using fed-batch fermentation manner; filling 2.6 L of liquid in the 5 L tank and controlling inoculating amount at 10%; dividing the fed-batch course as grading ladder type fed batch; controlling carbon source concentration of the fed-batch liquid as 100 g/L and ratio of acetic acid, lactic acid, propionic acid, and butyric acid as 1:1:3:3; adding nitrogen source with a concentration of 20 g/L in fed-batch manner at 12th hour; regulating pH value by automatically adding 3 mol/L of sodium hydroxide solution and 3 mol/L of hydrochloric acid solution in fed-batch manner, and controlling fermenting time at 60 hours; and (d) measuring PHA content: breaking wall of the freeze-dried cell with chloroform (every 10 ml of chloroform is added with 0.2 g of stem cell), preserving temperature for 24 hours at 60 degrees C, filtering, and naturally drying the filtrate to obtain PHA. An INDEPENDENT CLAIM is included for acetic acid, lactic acid, propionic acid, and butyric acid obtained by performing anaerobic acidification transformation to the organic wastes.