In order to obtain the present effective prestress and its longitudinal distribution of prestressed tendon during the process of inspection and evaluation, a unified analogue method was put forward. Based on the theory for calculating instantaneous prestress loss of the tendons with complicated geometry, a universal numerical model was established. Therefore, the distribution of effective prestress could be simulated after recognizing the nominal coefficients of prestress loss with the obtained stress data of objective steel tendon. The numerical simulation results of a full-length tendon of a three-span continuous beam bridge show that the relative errors between the calculated value and the value in the code are within 5%, which meets the requirement for engineering application.