Tin oxide is a unique material of widespread technological applications, particularly in the field of environmental functional materials. New strategies of fractal assessment for tin dioxide thin films formed at different substrate temperatures are of fundamental importance in the development of microdevices, such as gas sensors for the detection of environmental pollutants. Here, tin dioxide thin films with interesting fractal features were successfully prepared by pulsed laser deposition techniques under different substrate temperatures. Fractal method has been first applied to the evaluation of this material. The measurements of carbon monoxide gas sensitivity confirmed that the gas sensing behavior is sensitively dependent on fractal dimensions, fractal densities, and average sizes of the fractal clusters. The random tunneling junction network mechanism was proposed to provide a rational explanation for this gas sensing behavior. The formation process of tin dioxide nanocrystals and fractal clusters could be reasonably described by a novel model.