This paper aims to compare the difference of the corrosion behavior of SPHC steel under different service conditions. The outdoor exposure method is used to conduct dynamic and static exposure tests on SPHC steel for up to 18 months, and conduct sampling after 3, 6, 9, 12, 18 months respectively of exposure. Through corrosion kinetics test, SEM (scanning electron microscope), XRD (X-ray diffraction), electrochemical test, respectively, the average corrosion rate, corrosion product morphology, corrosion product composition and corrosion resistance of SPHC steel are evaluated after a certain period of atmospheric exposure. The results show that, after 3-month exposure, the corrosion rate and the thickness of the rust layer of SPHC steel after dynamic exposure are larger than those after static exposure, but are overtaken by those after 6-month static exposure. Subsequently, the corrosion rate of SPHC steel after both dynamic and static exposures slowly decrease, while the thickness of the rust layer gradually increase. The β-FeOOH and SiO2, which are rare on the surface of SPHC after static exposure, are detected on the surface of SPHC after dynamic exposure. The self-corrosion current of dynamic sampling is smaller than that of the static sampling at the same period, but the rust resistance is opposite. Due to the continuous changes in the service environment during the dynamic exposure process, the initial corrosion products of SPHC steel contain β-FeOOH and SiO2 impurities, which increase the reactive area on the initial sample surface and accelerate the initial corrosion. As the exposure time increases, although these impurities make it difficult for SPHC to form a uniform and dense rust layer like static exposure, the resistance of the rust layer improves, enhancing the corrosion resistance of SPHC , and inhibiting the occurrence of corrosion reactions.