Accurate　prediction　of　the　effective　pre-stress　in　steel　strands　is　of　great　importance　for　service　performance　assessment　in　pre-stressed　structures.　In　this　study,　a　new　parameter　for　characterizing　the　pre-stress　in　steel　strand　is　proposed,　named　energy　leakage　ratio　(alpha　EL)　of　ultrasonic　guided　wave　(UGW).　Firstly,　the　propagation　of　UGW　between　wires　of　the　strand　was　theoretically　analyzed.　Then,　finite　element　(FE)　models　of　steel　strand　were　established　and　laboratory　experiments　were　conducted　to　verify　the　effectiveness　and　accuracy　of　the　proposed　alpha　EL-based　pre-stress　evaluation　approach.　Results　show　that　alpha　EL　increases　linearly　with　inter-wire　contact　width.　alpha　EL　can　be　taken　as　a　new　parameter　for　strand　pre-stress　identification,　it　shows　a　high　linear　correlation　with　pre-stress　level,　no　matter　whether　the　excitation　position　is　located　in　core　or　helical　wire.　In　terms　of　numerical　and　experimental　results,　the　alpha　EL-based　pre-stress　evaluation　errors　are　within　3%　and　4%　respectively.　Compared　with　the　acoustoelastic　effect　based　and　nonlinear　ultrasonic　based　approaches,　the　alpha　ELbased　approach　showed　the　advantage　in　pre-stress　identification　accuracy.