It is known that the prominent southward z-component of the interplanetary magnetic field (IMF) sometimes reconnects with the geomagnetic field and causes major geomagnetic storms. Observing $B_{ z}$ (z-component of the IMF) between the sun and earth is one of the important clues for the space weather, but it is difficult to detect $B_{ z}$ before the arrival of IMF at the earth on the solar wind. Tibet ASγ reported that the sun shadow has the information of the y-component and average IMF strength. In this work, we will report the comparison of the $B_{z}$ and sun shadow observed by Tibet ASγ and discuss the possibility of remote sensing of $B_{z}$ using the sun shadow.