Working temperature, sensitivity, and selectivity are some of the characteristics of the applied gas sensors. How to design and fabricate an ideal gas sensor working at room temperature is still challenging and attracting lots of interest. Two-dimensional (2D) materials with ultra-thin structure have been demonstrated as a family of ideal candidates to achieve this goal. Among them, Ti C T MXene, a kind of layered sheet synthesized by selectively etching MAX phases materials, shows remarkable potential to be the sensitive materials solely or in a composite. However, their designing rules are still lacking critical thinking from the viewpoint of the intrinsic property of Ti C T MXene based materials. In this article, two critical features, i.e., the thickness of the sensitive materials, and the scope of the analytes, are elaborated towards Ti C T MXene based gas sensors after characterizing the performance of sensing reducing gases (NH and CO) and oxidizing gas (NO ). First, the thinner the Ti C T MXene sensitive layer, the better the sensitivity. Second, the Ti C T MXene based gas sensor is not suitable for strong and moderate oxidation gas due to its ease of oxidation. These two rules are demonstrated, and could be considered with priority both in the future researches and practical applications.