Understanding the characteristics of the solar magnetic field is essential for interpreting solar activities and dynamo. In this research, we investigated the asymmetric distribution of the solar photospheric magnetic-field values, using synoptic charts constructed from space-borne high-resolution magnetograms. It is demonstrated that the Lorentzian function describes the distribution of magnetic-field values in the synoptic charts much better than the Gaussian function and this should reflect the gradual decay process from strong to weak magnetic fields. The asymmetry values are calculated under several circumstances, and the results generally show two periodicities related to the variation of the solar B (0) angle and the solar cycle, respectively. We argue that it is the small-scale magnetic fields, the inclination of the solar axis, the emergence and evolution of magnetic flux, and the polar fields that are responsible for the features of asymmetry values. We further determined the polar-field reversal time of solar cycles 23 and 24 with the flip of asymmetry values. Specifically, for cycle 24, we assert that the polar polarities of both hemispheres reversed at the same time-in 2014 March; as to cycle 23, the reversal time of the S-hemisphere is 2001 March, while the determination of the N-hemisphere is hampered by missing data.