The invention discloses a transient electromagnetic logging device in a through-casing well, which comprises ground monitoring equipment (1), wherein the ground monitoring equipment (1) is connected with a downhole logging instrument (3) through a cable (2), and the downhole logging instrument (3) consists of a transmitting control unit (4), a receiving control unit (5), a magnetized power supply (6), a magnetizer (7), a transmitting coil (12) and a receiving coil (13). The device utilizes transient electromagnetic technology to transmit low-frequency high-power electromagnetic signals; according to Faraday law of electromagnetic induction, a variable magnetic field produces a variable electric field; the characteristics of an electromagnetic field are determined by the characteristics of medium; and the magnetic field which embodies the characteristics of the detected medium is received by the downhole logging instrument (3), so that the aim of identifying stratum characteristics through the signals detected by the receiving coil is achieved. The device has the characteristics of high efficiency, quickness and non-contact.