To quantitatively characterize the effects of copper film layers on the strain distribution and electrical properties of flexible electronic composite films under thermal loading, this study establishes an integrated testing system comprising a thermal deformation test workstation based on digital image correlation and an electrical testing station. First, two-dimensional horseshoe-shaped flexible electronic composite films with copper conductive layers of 50, 100, 200, and 500 nm thickness are prepared on flexible polymers via magnetron sputtering. In-situ and global deformation detection and electrical signal stability testing of the films are conducted under constant-rate heating conditions. The thermal strain fields of the two-dimensional horseshoe-shaped interconnections are extracted, with particular emphasis on analyzing the strain field characteristics per unit area near the copper film layers. The results show that the 500 nm-thick copper film layer exhibits the optimal compatibility with the substrate under thermal loading, leading to a stable overall strain trend in the sample. Electrical signal acquisition via the electrical testing station reveals that as the copper film thickness increases, the resistance of the 500 nm sample relaxes to 3 Ω and maintains excellent operational stability under sustained temperature loading. In conclusion, this study reveals the effects of different metal layer thicknesses on the thermal strain at the substrate-metal interface and signal transmission efficiency of flexible electronic composite films through the established thermal loading testing system. Experiments demonstrate the performance advantages of the 500 nm copper film layer sample under thermal loading, providing a theoretical basis for the safety design of stretchable electronic components.