To investigate the vibration characteristics of spring vibration isolating foundation for turbine-generator set, the modal tests are performed by model modal test method. A model of 8:1 of spring vibration isolating foundation for turbine-generator set for a 2×1 000 MW in Tianwan nuclear power plant units 3 and 4 is built up according to similarity theory, and then the test of dynamic characteristic is carried out by exciter method, and the natural vibration frequencies, mode shapes and damping ratio are acquired. The results of basic vibrating linear displacement under operation condition are obtained based on the vibration analysis of test data. The results show that the distribution of natural frequencies of structure was sparse in the vicinity of the operating frequency of 25 Hz by designing spring vibration isolating foundation. The maximum linear displacement of test point is 23.19 μm during the start-up and 11.73 μm during the operating speed range. Isolation efficiency of foundation are X-direction to 68.4％, Y-direction to 83.1％, Z-direction to 84.0％, which meet the requirements of Chinese specification "Dynamic machine foundation design specifications".