NOVELTY - A nanometer emission reduction biodiesel oil preparing method involves putting oil, petroleum acid, carbon alkyl, water, 120 solvent oil, methanol, fresh ammonia and multifunctional additive in a container. Air and gas source pressure are provided to the container. Inflation process is stopped. Biological oil, swill-cooked dirty oil or vegetable oil is added into the container. Acidified bio-oil, trench oil or vegetable oil is added into the container. The solution is adjusted to neutral in the container. The mixed solution is filtered to obtain the biodiesel oil.    USE - Method for preparing nanometer emission reduction biodiesel oil that is utilized for preparing universal diesel oil for a diesel engine of a motor vehicle (all claimed).    ADVANTAGE - The method enables obtaining biodiesel oil using convenient production process and a simple device.    DETAILED DESCRIPTION - A nanometer emission reduction biodiesel oil preparing method involves taking (in wt.%) oil (10), petroleum acid (5), carbon alkyl (5), water (30), 120 solvent oil (10), methanol (10), fresh ammonia (10) and multifunctional additive (5), and putting the materials in a container, where weight concentration of weak ammonia and water is 7%. Air is provided inside the container using a pipeline of 2-3 cm square. Gas source pressure is provided to a bottom part of the container through an air compressor. The container is placed for 5 minutes, and inflation process is stopped. 15% of biological oil, swill-cooked dirty oil or vegetable oil is added into the container. Acidified bio-oil, trench oil or vegetable oil is added into the container. The solution is adjusted to neutral in the container, where pH value of the solution is controlled between 6 and 7. The mixed solution is filtered to obtain a clear, transparent nanometer emission reduction biodiesel oil. An INDEPENDENT CLAIM is also included for a method for preparing universal diesel oil using nanometer emission reduction biodiesel oil.