Carbon/polymer based flexible electrothermal films due to the excellent formability, flexibility, light weight and cost-effectiveness are recognized as a promising alternative material compared to traditional metal based materials. In this work, a series of flexible electrothermal films were synthesized by incorporating pyrolysis N991 and multi-walled carbon nanotubes (MWCNTs) in polyethylene oxide (PEO) matrix with adding non-conductive SiO2 filler. The influences of SiO2 on morphology, microstructure and electrothermal performance of electrothermal films were systematically investigated. SiO2 filler guarantees the homogeneous dispersion of N991 and MWCNTs in PEO polymer matrix, which could prevent the unceasing migration of N991 and MWCNTs during the repeating heating-cooling cycles. The result shows that adding 5 wt.% SiO2 can achieve a stable electrical resistivity and excellent electrothermal reproducibility. Bending tests were employed to evaluate its superior mechanical flexibility. A new application was further developed to fabricate a flexible electrothermal film with a reversible thermochromic temperature-indicating function. (C) 2017 Elsevier Ltd. All rights reserved.