Flexible multifunctional polymer-based electromagnetic interference (EMI) shielding composite films have important application values in the fields of 5G communication technology, wearable electronic devices and artificial intelligence. In this work, Fe₃O₄/polyamic acid (PAA) nanofiber films are prepared by in-situ polymerization and electrospinning technology, and Ti₃C₂T_x nanosheets are deposited on the surface of the Fe₃O₄/PAA nanofiber films via vacuum-assisted filtration. Then, Janus Ti₃C₂T_x-(Fe₃O₄/polyimide (PI)) composite films are obtained by thermal imidization. The two sides of the Janus films exhibit completely different properties. The Fe₃O₄/PI side has excellent hydrophobicity and insulation property, and the Ti₃C₂T_x side has hydrophilicity and terrific conductivity. When the mass fraction of Ti₃C₂T_x is 80 wt.%, the Janus Ti₃C₂T_x-(Fe₃O₄/PI) composite film has excellent EMI shielding performances and mechanical properties, with EMI shielding effectiveness, tensile strength and Young’s modulus reaching 66 dB, 114.5 MPa and 5.8 GPa, respectively. At the same time, electromagnetic waves show different absorption shielding effectiveness (SE_A) when incident from two sides of the Janus films. When the electromagnetic waves are incident from the Fe₃O₄/PI side, the SE_A of the Janus film is 58 dB, much higher than that when the electromagnetic waves are incident from the Ti₃C₂T_x side (39 dB). In addition, the Ti₃C₂T_x side of the Janus Ti₃C₂T_x-(Fe₃O₄/PI) composite films also has excellent electrothermal and photothermal conversion performances. When the applied voltage is 4 V, the stable surface temperature reaches 108 °C; when it is irradiated by simulated sunlight with power density of 200 mW/cm², the stable surface temperature reaches 95 °C.