Abstract: In the middle and late stages of oil and gas field development, resistivity measurements are of great significance in assessing residual oil saturation in reservoirs. Traditional through-casing resistivity logging technology has drawbacks such as low efficiency, significant susceptibility to casing contact resistance, poor environmental adaptability, and limited detection depth. In contrast, transient electromagnetics, based on the theory of electromagnetic induction, emits transient electromagnetic fields without contacting the casing and measures changes in the induced electromagnetic fields of the formation to obtain formation resistivity parameters. However, the high electrical conductivity and high magnetic permeability of the casing can severely interfere with electromagnetic signals, affecting the measurement of formation resistivity. For this reason, this paper proposes a new method of using a combination of multiple coil systems to suppress the signal of casing in the pre-stress casing of formation response, and adopts finite element simulation to deeply explore the transient electromagnetic response curves as well as the transient electromagnetic radial probing depth and longitudinal resolution under the changes of different formation resistivity and casing parameters. The results show that this technique can effectively suppress the casing response in the pre-transient electromagnetic response, make the formation response clearer, provide accurate and reliable means for the measurement of formation resistivity in cased wells, and further enhance the accuracy of residual oil evaluation in oil exploration and development.