To overcome the drawbacks of high bulk density and bad applicability, in this study, straw ash was used as an additive to make unburned ceramsite which could be applied to sewage treatment. This method not only broadened the application of the unburned ceramsite and promoted unburned process, but also provided an economical and rational way to dispose fly ash and straw ash from power plant. The activity-excitation mechanism of fly ash, the function of primary components and the phase composition of ceramsite were studied in this research. The optimum process parameters were:5％ NaOH solution pretreat fly ash, and the ratio of the components were fly ash of 58.11％, calcium oxide of 4.84％, cement of 29.05％ and straw ash of 8％; The main characteristics index of ceramsite were shown as follows: bulk density of 785 kg/m³, specific surface area of 11.1 m²/g, broken rate of 2.3％. The ceramsite was tested on leaching toxicity and basic properties, and the results indicated that it was a proper way to make functional ceramsite of good property used in sewage treatment with straw ash as an additive raw material, and it achieved the purpose of economic energy conservation and waste treating.