Coal rich water was an important factor affecting safety production in coal mine, structural water conducting, roof water spraying and goaf water influenced safe advancing of working face, even caused mine flooding accidents. Therefore, principles and detection methods of transient electromagnetic exploration of water were introduced. Taking 11502 fully mechanized caving face as an example, transient electromagnetic method was used to prospect test, abnormal water zone in this working face was determined. Through drilling verification range, rich water was confirmed, which provided safety guarantee for smooth mining.