Abstract: The multipactor effect caused by electron harmonic multiplication in a microwave field is an important factor leading to the performance degradation of spacecraft. Carbon films have significant potential in reducing the risk of multipactor effects by suppressing secondary electron emissions. In this study, sub-micron carbon-based films of different thicknesses were deposited on copper surfaces by magnetron sputtering, and their secondary electron yield (SEY) was measured. The surface morphology, composition, and film thickness of the samples were analyzed and characterized using a scanning electron microscope. The multipactor threshold power of a parallel plate waveguide model was predicted using CST Studio Suite software. The results show that as the film thickness increases from 0 to 1239 nm, the maximum SEY decreases approximately exponentially from 2.18 to 1.72, and the second critical energy decreases from 2810 eV to 927 eV. When the thickness exceeds 938 nm, the maximum SEY tends to stabilize. Multipactor simulations show that when f·d = 5 GHz·mm, a 938 nm carbon film can reduce the multipactor power threshold of the parallel plate waveguide model by 21.27 kW. This paper deeply explores the quantitative relationship between SEY and carbon film thickness and predicts the application potential of carbon films in narrowing the multipactor sensitive range. It has important application value in suppressing the multipactor effect of spacecraft microwave devices and improving the space reliability of spacecraft.