A jointed mechanism of an electric wheelchair is disclosed. The jointed mechanism includes symmetrically arranged front caster assemblies, symmetrically arranged rear caster assemblies, drive wheel assemblies, and a main chassis assembly. The front caster assemblies are bushed to the main chassis assembly and the rear caster assemblies respectively. The rear caster assemblies are fixed to the drive wheel assemblies by pivot arm plate assemblies and bushed to the main chassis assembly and the rear caster assemblies to construct a four-bar linkage, which allows the electric wheelchair to always have contact with the ground with all wheels and to adjust the center of gravity to maintain balance automatically, even when the electric wheelchair is climbing a slope or moving on an uneven surface.