Calcium indicators are often used to monitor calcium signaling in cells and organelles, which include chemical calcium indicators and genetically encoded calcium indicators. With the development of technology and the continuous increase in research requirements, various versions of calcium indicators are constantly updated. The review systematically sorts out the existing calcium indicators, and introduces in detail the most widely used calcium indicators. Here, the advantages and disadvantages of existing calcium indicators are summarized, and the parts that can be optimized and improved are discussed. The aim is to provide some ideas for the further development of calcium indicator research.