The analysis of light variation of M87 can help us understand the disk evolution. In the past decade, M87 has experienced several short-term light variabilities related to flares. We also find that there are year-scale X-ray variations in the core of M87. Their light variability properties are similar to clumpy-ADAF. By re-analyzing 56 Chandra observations from 2007 to 2019, we distinguish the "non-flaring state" from "flaring state" in the light variability. After removing flaring state data, we identify four gas clumps in the nucleus and all of them can be well fitted by the clumpy-ADAF model. The average mass accretion rate is ∼0.16M⊙ yr−1. We analyze the photon index (Γ)–flux (2–10 keV) correlation between the non-flaring state and flaring state. For the non-flaring states, the flux is inversely proportional to the photon index. For the flaring states, we find no obvious correlation between the two parameters. In addition, we find that the flare always occurs at a high mass accretion rate, and after the luminosity of the flare reaches the peak, it will be accompanied by a sudden decrease in luminosity. Our results can be explained as that the energy released by magnetic reconnection destroys the structure of the accretion disk, thus the luminosity decreases rapidly and returns to normal levels thereafter.