The　effect　of　vibration　loosening　on　the　parametric　vibrations　of　inclined　cables　is　discussed.　By　the　equations　of　motion　considered　the　flexural　rigidity　and　sag,　vibration　loosening　is　numerically　calculated　by　the　finite　difference　method,　and　the　effect　of　vibration　loosening　on　the　principal　unstable　region　and　second　unstable　region　of　parametric　vibration　is　analyzed.　The　results　show　that　vibration　loosening　is　generated　first　at　the　lower　end　when　the　parametric　vibration　of　inclined　cable　occurs.　The　minimum　support　excitation　that　generates　a　compressive　force　varies　with　inclination　angles.　Under　the　support　excitation　with　small　amplitudes,　vibration　loosening　easily　occurs　in　the　second　unstable　region　of　cables　with　a　small　inclination　angle.