  We present the long-term optical spectroscopic observations on the Be/X-ray
binary A0535+26 from 1992 to 2010. Combining with the public V-band photometric
data, we find that each giant X-ray outburst occurred in a fading phase of the
optical brightness. The anti-correlation between the optical brightness and the
H$\alpha$ intensity during our 2009 observations indicates a mass ejection
event had taken place before the 2009 giant X-ray outburst, which might cause
the formation of a low-density region in the inner part of the disk. The
similar anti-correlation observed around 1996 September indicates the
occurrence of the mass ejection, which might trigger the subsequent disk loss
event in A0535+26.
