The high-temperature (T ≥ 20 K) magnetic properties of dysprosium iron garnet (DyIG) are theoretically presented in strong magnetic fields based on three-sublattice model. Under the consideration of the molecular fields among the different magnetic sublattices, our theory confirms that the magnetization in DyIG shows obvious isotropy with the increase of the temperatures. Also, at higher temperatures, the variations of the magnetization in DyIG with the magnetic fields (He) and the temperatures (T) are successfully fitted. Similar with the conclusion at low temperatures, it is also proved that the contribution of the magnetization of the rare-earth magnetic sublattice to the total magnetization in DyIG is greater than that of iron sublattices at higher temperatures. In addition, theoretical calculations reveal that the temperature and field dependence of the coefficients αi (i=a, c and d) associated with the molecular field parameters λ and magnetic susceptibility χ, and at higher temperatures, it can be described as αi=P1+P2/He where P1 and P2 are the coefficients.