The interplanetary magnetic field(IMF) between the Sun and the Earth induces the displacement
of the cosmic-ray Sun shadow from the optical position. LHAASO is a large hybrid extensive
air shower (EAS) array at Haizi Mountain, 4410 m a.s.l., in China. It is composed of three
sub-arrays. The one square kilometer array of LHAASO operated since the end of 2019 and
denoted as LHAASO-KM2A, can observe the Sun shadow with a daily significance exceeding
5 standard deviations which is crucial to monitor the variation of its displacement. Using the
daily Sun shadow observation achieved by LHAASO-KM2A at the energy ∼ 40 TeV and the IMF
measurement achieved by OMNI at 1AU in 2021, we found that there was a good cross correlation
between them while the variation of the former was ∼ 3 days earlier than that of the latter on
average. This made it possible, for the first time, to measure the daily 𝐵𝑦 of the IMF reaching
1 AU position in advance with the daily monitoring of the Sun shadow. In addition, combined
with the simulation, the time advance is found to be related to the spiral structure of the IMF and
its different observation positions. This implies the possibility of using time advance to diagnose
Parker’s model in the future.