To improve the ionic conductivity and electrochemical performance, a cement-based composite electrolyte with high ionic conductivity and good mechanical strength was synthesized by using room temperature ionic liquid 1-butyl-3-methylimidazole bromide (BMIMBr) as redox active additive, which can be applied to construct structural supercapacitor. The results show that the ionic conductivity of cement-based composite electrolyte containing 20% (mass fraction) BMIMBr reaches the highest value of 35.91 mS·cm-1. BMIMBr can provide Br- which can produce reduction reactions and increase the number of free ions, which is beneficial for ion transport in electrolyte and obtains higher specific capacitance. The structural supercapacitor shows a high specific capacitance of 20.07 F·g-1 at a current density of 0.05 A·g-1. After 1 000 cycles of galvanostatic charge-discharge, the capacitance retention rate reaches 83.6% and coulomb efficiency is 97.56%, demonstrating an excellent cycle lifespan.