A strain modal testing method has been applied to a cantilever beam to investigate the characteristics of the method. By applying the method to an analytical and an experimental system, it was shown that accurate modal parameters can be estimated from strain frequency response functions using a current modal parameter extraction algorithm. The modal parameters estimated by the method are more accurate than those by the conventional method which uses accelerometers when the tested system is of light weight. The method can be used to predict strain responses and excitation forces for given excitation forces and responses, respectively. Cracks on a structure can be detected by measuring strian FRFs and comparing them with the original ones.