With the help of modal experiment,the free support of specimen mounted on experimental apparatus proposed in this paper was verified firstly.Then,the first order natural frequency of specimen was measured by transient excitation and the modulus of elasticity of dimensioned SPF lumber was calculated.According to GB50005-2003"Code for design of timber structures",the probability of modulus of elasticity of this batch of SPF dimensioned lumbers reaching Ⅱc level is 96.3%.The transient excitation frequency method is rapid,simple and reproducible and has high accuracy.So,it is applicable for testing in industry of light wood frame construction.