In order to obtain raw material locally and make optimal use of fly ash in engineering construction in loess areas, we conducted a series of dynamic triaxial tests on unsaturated remolded loess specimens that had been modified with different proportions of fly ash. Based on the test results, we studied the seismic subsidence properties of loess based on the improvement afforded by the fly ash, and derived change laws for the dynamic modulus of deformation and the dynamic residual strain for different proportions of fly ash. The results show that the quantity of dope in fly ash significantly influences the seismic subsidence properties of loess. The changes in the dynamic modulus of deformation and in the dynamic residual strain vary with respect to the improvement afforded by fly ash under the same consolidation stress, i.e., the former becomes larger while the latter become smaller and the relationship between them is well described by the power function. Moreover, we verified that the anti-seismic subsidence behavior of the loess specimens was much better when the proportion of fly ash is about 20%. Thee research findings provide a scientific basis for establishing anti-seismic designations for foundations in loess areas, and thus have important application value.