This paper intends to develop geopolymer-based composites for geothermal energy applications. Both silicon carbide (SiC) sand and SiC powder were applied to optimize the thermal and mechanical behaviours of geopolymer. The flexural and compressive strength of geopolymer composites with different mix designs were investigated. A novel test set-up to record the thermal conductivity were designed, and the thermal behaviours of geopolymer composites with different mix design were tested. It was found that the proper addition of SiC powder is conducive to the compressive and flexural strength of geopolymer composites, while the influence of SiC particles is insignificant. The relationship between flexural and compressive strength of geopolymer composites was also investigated, and it was found that the Portland cement association (PCA) code reached the best fitting precision. With the addition of SiC materials, the maximum thermal conductibility of geopolymeric composite can be as high as 5.35 WmK, which is about five times higher than conventional cementitious composite. The combined application of SiC powder and SiC particle is practical to increase the thermal conductivity of geopolymer, making it a suitable material for geothermal energy applications. Based on the numerical model, it was concluded that the addition of silicon carbide is beneficial to the heat exchange rate of the energy pile and improves the heat utilization efficiency of the energy pile.