This paper studied the stability and regeneration mechanism of photocatalyst Bi20TiO32. There is no change in the XRD of the catalyst after reaction, which indicates that photocatalyst Bi20TiO32 has stable structure. The comparison of XPS between used and fresh catalyst, shows that the major cause of the deactivation is the competitive adsorption of intermediates onto the surface active sites of the catalyst. Simple cleaning by deionized water, light irradiation, acid or base purging can not refresh the catalyst. However, ethanol with ultrasonic vibration can recover its activity well, as further demonstrates that the deactivation is because of that active sites are occupied by organic intermediates. Calcination is an effective way to recover the catalyst activity.