We show that 1f noise of charge fluctuation at disordered surfaces follows naturally from random hopping of electrons among localized states. Computer models are proposed with hopping mechanisms simplified, and the occurrence of 1f α power spectrum is robust. The lifetime distribution of electrons is found to be D(τ) = τ - β and a connection between the lifetime distribution and the power spectrum is derived. It is shown that the 1f noise comes from random superposition of oscillatory spectra. We also define an generalized random walk model to act as the underlying mechanism of 1f noise in disordered systems.