Detections and manipulations of quantum optical state at single-photon level have received much attention in the current experiments. Here, by numerically calculating the time-evolved Wigner functions, we investigate the dynamics of the typical non-classical state, i.e., few-photon superposition states in a dissipating optical microcavity. It is shown that the negativity of their Wigner function vanishes with dissipation. But this does not imply that all the non-classical features of the dissipative quantum state disappear. In fact, it is shown that the value of the second-order correlation function g(2)(0) (which serves usually as the standard criterion of a typical non-classical effect, i.e., the anti-bunching of photons, if g(2)(0)g(2A)(0) varies with the cavity dissipation and thus could be used to describe the physical effects of the dissipative cavity. Finally, we discuss the experimental feasibility of our proposal with a practically-existing cavity QED system.