The deposition of combustion ash on the inner surface of the incinerator wall and the bed materials in a fluidized bed hinder the stable operation of sewage sludge incineration plants and damage the relevant facilities. Ash particles comprise various main and trace elements and form complex chemical compounds. Removing certain elements during the combustion of ash particles is impossible when discussing the effect of the target element on ash adhesion at high temperature. Herein, to analyze the effects of certain elements on ash adhesion, we prepared model ash particles containing the target elements by using pure nanosized particles and chemical compounds. We focused on seven main elements, i.e., Si, Al, Ca, Mg, Na, K, and P, present in real sewage sludge ash and synthesized the model ash with almost the same chemical compounds as those in real combustion ash without the trace elements. The adhesion property of each ash particle was characterized based on the tensile strength of the ash powder bed developed in our previous study, and the synthetic ash showed a similar adhesion property to that of the real ash under high temperature. To discuss the effects of Ca, Mg, and Al on the adhesion behavior, two types of model ash with only five elements, Si, Al, Na, K, and P, were prepared, and their adhesion behavior at high temperature was characterized. In this model ash, Ca and Mg were replaced with Al, and the other elements were fixed at the same concentration as that in the seven-element ash. The tensile strength of the five-element model ash was greater than that of the seven-element model ash. The equilibrium calculation and FE-SEM results before and after heat treatment suggest that the existence of Ca and Mg is important to stabilize phosphorus-rich sewage sludge combustion ash at high temperature.