Solar activity phena includes not only the phenomena which are driven by solar surface magnetic fields, but also the phenomena such as evolutions of total luminosity, rotation, symmetry and so on. It is very important to study the periodicity of these phenomena as their periodicity may imply some physical mechanism that result in the phenomena. The first discovery was that the flare occurrence rate had a 154-day period in 1984, and after that this period was found in many kinds of solar active phenomena. Besides the 11-year cycle of solar activity and 27-day period of solar rotation, the 154-day period has become one of the most famous periods. This paper summarizes the progress in the study of the 154-day period in these phenomena. Some unresolved problems and highlights are also discussed.