The investigation of magnetization of digital alloys is presented with a model calculation, based on the structural characteristics of digital alloys that contain quasi-two-dimensional ferromagnetic islands and randomly distributed Mn ions. In addition to the spin-exchange interaction between a free carrier and a randomly distributed Mn ion, the interaction between a carrier and an island, and ferromagnetism of each island are taken into account simultaneously. In this model, the exchange interaction between free carriers and islands is ferromagnetic, based on energy minimization. This interaction occurs because of the carrier wavefunction penetration into the islands, which is treated empirically with an effective exchange constant. This model produces temperature-dependent magnetization as a function of external magnetic field qualitatively and shows the magnetization reversal of digital alloys at certain temperature range. The magnetization of digital alloys also strongly depends on the carrier and Mn ion concentrations and distribution of Mn ions in the system.