MAX phases are a group of layered ternary carbides and/or nitrides. M is an early transition metal, A is mainly an element in ⅢA, ⅣA and ⅤA groups, and X is C and/or N. These compounds have characteristics of both ceramics and metals, such as excellent conductivity, thermal conductivity, corrosion resistance and antioxidant properties. And they have potential applications in many fields. In recent years, many MAX phases with new elements, new structures and solid solutions appear and then enrich the family of MAX phases. The MAX phase solid solutions are obtained by adding elements into the crystal structures of MAX phases. 127 MAX phase solid solutions which can be divided into four types are summarized in this paper. The structural change and performance regulation of MAX phase solid solutions are analyzed, and the existed theoretical problems and the key technologies that need to be solved urgently are pointed out. Finally, the research directions and developing trends of MAX phase solid solutions are prospected.