Abstract: Composite electrode materials with 60% mass fraction of RuO₂ loading on activated carbon (AC) were prepared by a modified colloidal method, then it was annealed at different temperatures for 6h.The cyclic voltammetry, constant charge-discharge and alternating impedance of the composite electrode materials were measured by electrochemical working station. The morphology and structure of the composites annealed at different temperatures were characterized by SEM, EDS and XRD. The results illustrate that the specific capacitance is the best at 240 ℃ and its value is 445 F/g with good charge-discharge performance. The impedance value gradually decreases with the increase of annealing temperature under 240 ℃ and increases slightly beyond 240 ℃. Morphology of composite annealed at 240 ℃ is fine and homogeneous hydrated RuO₂ particle distributed in the carbon matrix. The RuO₂ of complexes remains amorphous, and changes to the crystal phase when the temperature is beyond 270 ℃. Electrochemical properties of the composite electrode prepared by the modified colloidal method is good when it is annealed at 240 ℃.