This study tries to obtain the spring constant of welded metal bellows through experimental and numerical method respectively. The prediction of spring constant plays a great role in the design and application of the welded metal bellows. To derive the spring constant of the bellows, we employ commercial package to build up 2 axi-symmetric FEM models by using plane 42 and shell 51 elements. In the experiment, we use UTM to measure the spring constant of the bellows. And, the predicted spring constant resulting from the analysis is compared with the experimental one to discuss the rationality of spring constant analysis. The analytical results correspond well with experimental data and hence explaining the validity of FEM model.