In normal TEM sounding,the parameter of secondary induced voltage V signal is collected by using magnetic induced coil;however,the late signal is usually too weak to identify deep buried target.In this paper,direct measuring of B field parameters is used to test its practical effect.Firstly,from the response of B field and dB/dt and numerical calculation of different models,we can see that the B field has superiority in late time detection.Then the SM24 TEM system which is used to measure B field and the GDP-32 system which is adopted to measure induced voltage are compared with each other.With the same observation parameters,B field data are more superior than induced voltage data.The characteristic frequency of fluxgate sensor is relatively low and it decays slow.In addition,the amplitude of B field data is larger than that of dB/dt data.This means is favorable for measurement in late time because the influence of low resistivity covered layer on it is relatively low.The results show that developing and using fluxgate sensor is an important direction to resolve fine TEM exploration.