When　appropriate　parameters　are　selected,　coupled　SD　oscillators　can　exhibit　bistability,　tristability,　and　even　quadrastability.　The　presence　of　multiple　potential　wells　introduces　rich　dynamical　characteristics　into　these　multi-stable　systems.　As　a　result,　global　dynamical　analysis　of　quad-stable　systems,　particularly　the　study　of　subharmonic　orbits,　has　garnered　significant　attention　in　recent　years.　This　paper　aims　to　investigate　subharmonic　motion　in　the　quad-stable　system　of　coupled　SD　oscillators　and　to　establish　a　theoretical　framework　for　Melnikov　analysis　of　Type　I　subharmonic　orbits.　Based　on　the　derived　Melnikov　function,　the　existence　of　Type　I　subharmonic　orbits　is　verified.　Finally,　numerical　simulation　methods　are　employed　to　validate　the　proposed　approach　by　plotting　phase　portrait,　the　time　history　diagram　t　−　x　and　spectrum　diagram.　©　2024　Institute　of　Physics　Publishing.　All　rights　reserved.