The sandwich-structured PMMA-ANF-PMMA (P-A-P) composite film was constructed using vacuum impregnation method based on aramid nanofibers (ANF) and poly(methyl methacrylate) (PMMA) for preparing high dielectric breakdown strength polymer materials over a wide temperature range. The results showed that the P-A-P composite film exhibited a distinct three-layer structure, and the thickness of PMMA layer increases gradually with increment of PMMA concentration. Additionally, the dielectric constant and dielectric loss of the P-A-P composite film decreased with the increase of PMMA concentration. Due to the reduced surface roughness, enhanced Young"s modulus, and the special spatial electric field distribution mechanism in the multilayer structure, the dielectric breakdown strength of P-A-P composite film continuously increased with enhancement of PMMA concentration. When the PMMA solution concentration was 10 wt%, the dielectric breakdown strength of P-A-P composite film at 25°C and 120°C were 262.4 MV/m and 232.8 MV/m, respectively, which were 87.8% and 134.0% higher than that of single-layer P-A-P-0 (ANF film), providing a new approach for preparing polymer materials with high dielectric breakdown strength over a wide temperature range.