This article summarized the choroidal thickness systematically and followed by relevant findings which describes the influencing factors of the choroidal thickness, the changes of the choroidal thickness in ophthalmic diseases and the relationship between the blood flow and the choroidal thickness detailedly. Choroidal thickness is affected by many factors, such as age, gender, intraocular pressure, refractive error, axial length, systolic blood pressure, daily rhythm, body position, smoking history, etc., and choroid is significantly correlated with many ophthalmic diseases. Choroidal thickness is of great importance in the diagnosis and treatment of ophthalmic diseases.