Abstract: Conductive polymer composites (CPCs) are widely used for the preparation of electromagnetic shielding materials due to their good comprehensive performance such as good corrosion resistance, high specific strength, low cost and easy processing. In this paper, MXene-carboxylated carbon nanotube/polyimide (MXene-CCNT/PI) composite films with good comprehensive performance were prepared by a simple scraping and thermal imidization method. The synergistic action of MXene and CCNT constructed a good conductive network, which gave the films high efficient electromagnetic shielding performance (EMI SE). When the contents of both MXene and CCNT were 12.5wt%, the film thickness was 80 μm, the conductivity was 5.88 S/cm, the EMI SE was 26.49 dB, and the ratio of electromagnetic shielding effectiveness to thickness (EMI SE/t) was 331.13 dB/mm. Moreover, the film showed long-lasting and stable EMI SE under extreme environments (acid-alkali treatment, high and low temperature treatment, and repetitive bending). At the same time, the MXene-CCNT/PI film still have a tensile strength of 53.17 MPa, excellent thermal stability (>500℃), and flame retardancy. Convenient and efficient preparation of polymer-based EMI shielding composites is realized, taking into account their excellent mechanical properties and heat resistance.