The phosphoric acid-based geopolymers were synthesized using chemosynthetic Al2O3-2SiO2 and phosphoric acid at ambient temperature, curing for 28d at room temperature. The influence of the water from the geopolymer materials on the dielectric properties was investigated. The phase’s transformation was measured by XRD. The amorphous SiO2 from unreacted particles transformed to quartz crystal at 950 °C when exposure to 1350 °C, some mulite appeared, however, the dielectric properties change a little. After the geopolymer materials were heated at 350 °C, its dielectric loss could depress down to lower level of 10-3.