The capacitance loss caused by slow electron and ion migration kinetics in thick electrode with high-mass loading has been regarded as a great challenge in the field of electrochemical energy storage. Herein, we demonstrate a facile electrochemical deposition method for coating the heterostructured Ti₃C₂T_x/WO_x onto flexible carbon cloth (Ti₃C₂T_x/WO_x@CC). In the Ti₃C₂T_x/WO_x heterojunction, the mixed-valence WO_x core provides abundant active sites for H⁺ ions accommodation, while Ti₃C₂T_x shell can not only prevent peeling off the thick WO_x but also act as an interconnected conductive network. The Ti₃C₂T_x/WO_x@CC flexible electrode with an ultrahigh mass loading of 34.9 mg·cm⁻² exhibits a high areal capacitance of 5.73 F·cm⁻² at 5 mA·cm⁻² and excellent rate capability. Notably, the Ti₃C₂T_x/WO_x@CC electrode under such a high mass loading still delivers a gravimetric capacitance of 164 F·g⁻¹ and areal capacitance of Ti₃C₂T_x/WO_x@CC electrode increases linearly with the WO_x mass loading. Furthermore, a symmetrical supercapacitor assembled with Ti₃C₂T_x/WO_x@CC electrode exhibits a good areal energy density of 96.8 μWh·cm⁻² at a power density of 1.5 mW·cm⁻². This work verifies high mass loading of active materials per unit electrode area for charge storage of supercapacitors in limited space, indicating the great potential in the development of commercially available thick metal-oxide film supercapacitors.