Abstract: The surface morphology and mineral composition of Mars attest to the past presence of fluid water. Recent research reveals the existence of large amount of water in Mars Polar Caps and subsurface. In the past 12 years, the Martian subsurface has been probed by orbital radar sounders, the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on ESA's Mars Express, and the Shallow Subsurface Radar (SHARAD) on NASA's Mars Reconnaissance Obiter. Both have been successful and obtained a series of scientific achievements. Martian subsurface is believed to have recorded the important massage about the history of Mars. Probing and studying the Martian subsurface could help revealing the formation and revolution of Mars and searching for Martian life. We described the research status about Martian subsurface in this overview, introduced the operation principle of the space-based penetrating radar, and presented the key findings of MARSIS and SHARAD, which have provided a new insight into many aspects of the history and environment of the planet. We also introduced several future Martian subsurface radars in this paper.