Abstract: The principle of improved method for calculating particle size tested by light transmission is to use the inherent sedimentary height of the same kind of powder with various sizes. A "curve plate of temperature-sedimentary height" is made according to the inherent height, ensuring each point on the curve plate to coordinate powder sedimentary curve recorded with meter in order. Thus, it is very convenient to read out the light transmission amount of each particle diameter required for powder to be tested. This method emits the tedious calculation programa for determining sedimentary height of each particle diameter of testing powders and will save the time to calculate and gather data points bY about 80% with height accuracy and less errors.