Abstract: Marine controlled source electromagnetic (MCSEM)detection uses the relationship between the electric or magnetic field in sea water and the conductivity of seabed to obtain the media information of seabed, so as to study the submarine internal composition and structure. This paper presents a method to calculate the time domain electromagnetic response by frequency domain electromagnetic response, and analyzes the influence of off-time on the response of time-domain electromagnetic detection of marine controlled source with central loop device by simulation. The results show that the off-time of the transmitter current of time-domain controlled source electromagnetic detection not only influences the amplitude of the early received signals, but also affects the resolving power to the media in the shallow seabed.