Abstract: Several papers have given the pilot study of transient electromagnetic(TEM) field signals using joint time-frequency analysis(JTFA).However,all the JTFA methods have their advantages and disadvantages,and for deep insight the information in TEM the comparison between these methods and newly presented S-transform is necessary.This paper first uses S-transform and generalized Stransform processing transient electromagnetic(TEM) signal.Secondly,gives a method of evaluation instantaneous frequency(IF) using S-transform and give the result of the comparison.Thirdly,it gives a character of TEM diffuse by using IF.In the end this paper discuss the denoise in S-domain.