In order to effectively evaluate the loss of pre-stress in the in-service steel strand, a guided wave nondestructive testing method for identifying the tensile force of the steel strand is proposed. Numerical simulations and experiments of ultrasonic guided wave (UGW) propagation are carried out on steel strands with different tensions. The multi-scale energy entropy of UGWs is used as the feature vector to construct tension identification index, and the influence of propagation distance and acquisition method is analyzed. The results show that the multi-scale energy entropy of guided waves differs significantly under different tensile forces. An obvious linear relationship which is less affected by propagation distance and acquisition method between the identification index and tension can be found. Compared with the finite element results, the measured propagation distance of the identification index increased by 957.69%, and the sensitivity coefficient increased by 20.3%. The sensitivity of identification index grows with the increase of propagation distance, but the growth rate is opposite. The acquisition method of center wire excitation and center wire receiving is more sensitive to the change of tension.