Abstract: Radar with Time Domain Pulse Mechanism is widely used to detect the Earth, the Moon as well as explore deep space. The research of radar penetrating depth when it is working is useful to analyze whether the target is within the detection range. Traditional calculation methods are mostly based on the classic radar transmission equations. In actual terms, priori assumptions about the subsurface structure and dielectric properties of the medium have to be made, then the penetrating depth can be calculated in theory. In order to overcome such limitations, this paper presents a new method, which does not require any priori assumptions. It calculates the depth by using the correlation between data from real radar detection only. This paper introduces two correlation coefficient methods: one is wavelet method, and the other is trace-correlation method. Using simulations we have verified the validity of the two methods. We also discuss the limitations of these two methods in the paper. Our work should serve as an important solution for penetrating depth calculation of time domain pulse radar in future studies.