Abstract: The article explains methods of density disturbance rejection,laboratory graduation and field graduation starting from technique principle of relationship between gamma-gamma response and atomic number,effective atomic number,and so on.It is clear by analysising that this method is a atomic number response disturbed by density.Series modular graduation technique can reject the density disturbance and set up response of Pe value and U value.After data are normalized by site simple modular graduation,it can do quantity interpretation of coal ash contains on certain condition.