The invention provides an extract of total flavonoids of coromandel coast falsemallow. The weight percent content of the total flavonoids is no less than 1% by taking the weight percent of rutin as a reference. The invention further provides a preparation method and an application of the extract. The extract is stable and controllable in quality as well as simple and feasible in extraction process and cannot perform pollution on the environment, thereby being suitable for large-scale extraction. The extract is used for treating prostatic diseases, and particularly has definite and safe medicinal effects for treating prostatic hyperplasia, prostatitis, prostatic cancers and abacterial prostatitis, thereby providing a new medicine selection for clinical applications.