90Sr is interest in the fields of environmental and health. In order to carry out the applications of 90Sr, the AMS measurement method of 90Sr with the ion energy of 98.5 MeV has been developed at CIAE. The AMS measurement method of 90Sr is systematically studied from the negative ion extraction, the unique isobaric separation technology with Q3D magnetic spectrometer and the ion identification method with multi anode gas ionization chamber. The interference is effectively eliminated and the background level of 90 Sr/Sr = (9.2 ± 1.8) × 10-13 has been achieved. It lays a foundation for carrying out the applications.