•Design strategies of g-C3N4 polymer photocatalyst are reviewed.•High stability and non-toxic are the characteristics of g-C3N4.•Advantages and applications of g-C3N4 in photocatalysis are summarized in detail.•Methods for improving photocatalytic performances of g-C3N4 are discussed.•Challenges of large-scale application of g-C3N4 based on photocatalysts are presented. Graphitic carbon nitride (g-C3N4) is an excellent polymer photocatalyst to revolutionize the semiconductor field and deprive solar photons from their energies for conversion into chemical energy resulting in degradation of a number of hazardous organic pollutants into harmless compounds. g-C3N4 has fortified its applications in the field of photocatalysis due to its unique nature including high chemical stability, non-toxic and suitable position of energy band. However, its relatively low visible light absorption, quick recombination of excited charges and low surface area have over shaded its full-fledged efficiency in the above mentioned fields. In this review, we have highlighted its advantages and applications in the field of photocatalysis and provided an updated discussion on the different ways to improve its efficiency, especially its visible light absorption and excited charge separation.