Abstract: There were A and B different fly ashes with the Si/AI ratio of 2.01 and 1.28 individually selected as the study objects in order to investigate the coal ash deformation conditions in the high temperature tubing boiler and to draw the area of the high temperature column with the temperature variation curve.The paper discus sed the influence of the Si/AI ratio to the thermal expansion of the fly ashes.The results showed that the expansion degree of the A coal ash would be more obvious tha n the B coal ash and the initial shrinking temperature of the A coal ash would be higher than the B coal ash.When the A and B coal ashes were individually added with t he quantity fraction 10%、20%、 30% of Fe203、CaO、MgO, the A coal ash would have an obvious expansion, a small shrinking degree and large and density gas hole s on the surface of coal ash slag and the expansion degree of the B coal ash would be small, the shrinking degree would be high and the gas holes on the surface slag would be less.The liquid phase quantity occurred at the combustion initial period of the coal ash column with a different Si/Al ratio would be high in different which could cause different gas residual in the high temperature coal ash column and would cause a different shrinking and expansion of the different Si/AI ratio coal ash column un der the high temperature.