To solve the restacking of the Ti3C2Tx nanosheets and destroy of electrode microstructure during cycles and gain high-performance electrode for supercapacitors, Ti3C2Tx/PDA composite film electrode was rationally designed and successfully synthesized by one-step in situ polymerization of dopamine on the surface of the Ti3C2Tx nanosheets. The as-synthesized Ti3C2Tx/PDA composite electrode achieved a superior areal capacitance of 715 mF/cm2 at a scan rate of 2 mV/s and maintained 95.5% of initial capacitance after 10000 cycles, exhibiting long-term cycling stability. The areal capacitance can be enhanced to 3440 mF/cm2 when the mass loading increases to 13.6 mg/cm2. The improved electrochemical performance and outstanding electrochemical stability can be attributed to the effective suppressing the restacking of Ti3C2Tx sheets and increasing interlayer spacing by introducing PDA, which could be beneficial to expose more surface active sites, shorten the diffusion path of electrolyte ions, promote electron transport and fast Faradaic reaction. Our work opens new design space to develop the high performance negative electrode materials.