A real-time, nondestructive mid-infrared (mid-IR) platform was proposed for isotopic methane detection. The measurement system consisted of a tunable mid-IR laser, a miniaturized gas chamber, and a mid-IR signal receiver. The isotope ratio of the 12CH4/13CH4 was identified by measuring the mid-IR spectrum at λ=3.2-3.5µm.In-situ12CH4/13CH4 monitoring was then achieved by tracing the characteristic mid-IR absorption peaks assigned to the 12CH4 at λ=3.328µm and 13CH4 at λ=3.340µm. The real-time methane isotope analysis can be applied to environmental monitoring and petroleum industries.