The polymer semiconductor g-C3N4 has attracted widespread attention in fields such as pollutant degradation and clean energy production due to its features such as narrow band gap, high stability, low cost, etc. However, there are some drawbacks of g-C3N4 that it has low charge separation rate, high charge recombination rate, etc., which lead to its unsatisfactory photocatalytic ability. Therefore, improving the photocatalytic performance of g-C3N4 has become a research hotspot in the field of photocatalysis. The g-C3N4-based photocatalysts prepared by heterojunction construction, elemental doping and other modification methods can enhance the absorption of visible light and have strong photocatalytic ability, which have wide industrial application prospects. In this work, firstly, the research actuality of g-C3N4-based photocatalysts was briefly introduced. Secondly, this work discussed the research status of preparation methods and introduced several preparation methods for g-C3N4. It also explained the problems that should be paid attention to when applying different preparation processes. In addition, various mechanisms of the approaches to improve its photocatalytic performance were illustrated, and the development directions were pointed out, summarized and prospected. In the follow-up research, if the advantages of material science and environmental science can be effectively combined to prepare g-C3N4-based photocatalyst composites with stable structure and excellent photocatalytic performance, it will be of great significance to improve practical value of g-C3N4.