Using the vector magnetic field data from the Huairou Solar Observing Station of Beijing Astronomical Observatory, we study their size-flux relations for various magnetic elements identified as pores and spots. More than 725 pores and spots which located near the central meridian are selected. The power-law relationships for the mature sunspots are derived, and, there are different power-law relationships for the different magnetic elements. We also find that there are not evident relations between size and flux of the pores and protosunspots. Such the results may be useful for understanding the physical conditions and dynamical processes of magnetic flux tubes in the solar plasma during the sunspot's formation. In addition, their characteristic size is also given.