As one of the major short chain hydrocarbons resulting from the cracking process, ethylene is often used as a surrogate for cracked kerosene. In this study, a skeletal mechanism of ethylene was developed under the typical working conditions of scramjet combustors. The skeletal mechanism was reduced from a fully verified detailed mechanism under the desired working conditions. An integrated reducing method containing directed relation graph with error propagation method (DRGEP), sensitivity analysis (SA), and computational singular perturbation (CSP) was employed to obtain three skeletal mechanisms. A three-level fidelity validation of the skeletal mechanisms respectively comparing the kinetic properties, the global combustor performance, and the detailed flame structure was proposed to comprehensively evaluate the skeletal mechanisms. In the first-level fidelity validation, the three skeletal mechanisms all show good agreement with the detailed one in the autoignition delay and laminar flame speed over a wide range of working conditions. Then in the second-level fidelity validation, the smallest mechanism consisting of 24 species and 86 reactions (24S/86R) was further validated through incorporating with the large eddy simulation of a realistic scramjet combustor. Comparisons with the experimental data and the predictions by the detailed mechanism show that the global combustor performance (e.g., pressure, Mach number, and combustion efficiency) was accurately predicted by the 24S/86R mechanism. In the third-level fidelity evaluation, the flame structure characterized by the distribution of CO, OH, and heat release rate was analyzed through comparing the predictions by the 24S/86R mechanism with those by the detailed one during which the insufficiency of the skeletal mechanism was also recognized.