Abstract: The invention put forward an improved method for isotope dilution analysis of strontium using mass spectrometer. The sample of strontium is measured by a multi-collector mass spectrometer which equipped with no less than five collectors. The isotopes of strontium are statically collected by the collectors: ion beams with different mass numbers will be collected by different collectors. The voltages of the outputs of the collectors are read and amplified by a dynamic virtual amplifier. Then equations which include some variables and the output voltages of every amplifiers are established. The solutions of the equations will be the isotope ratios of the sample being measured. The invention can combine two analyses, one for isotope ratio and the other for concentration of strontium, together into one so that the measurement procedure is simplified.