Excessively high laser power density of the fiber core causes nonlinear effect and laser damage, which limits the output power enhancement of the fiber lasers. Using the multi-core fiber is one of the most effective schemes to solve this problem. The selection of in-phase supermode and the fabrication of multi-core fiber are the key factors for limiting the progress in multi-core fiber lasers. Therefore, how to realize a multi-core fiber with a large mode area and an in-phase supermode has attracted the attention of domestic and foreign researchers in recent years. The latest progress in mode selection and fabrication technology for multi-core fibers is illustrated, and the development prospect of realizing high power single-mode multi-core fiber lasers is proposed by evaluating the feasibility of several technical solutions.