There　is　micro　shock　signal　lower　than　0.01　Hz　in　the　low-speed　and　heavy-duty　gearbox　and　it　is　difficult　to　extract.　It　has　become　a　difficult　problem　for　the　fault　diagnosis.　In　this　article,　the　trend　graphs　of　the　saltation　coefficient　of　wavelet　analysis　and　indirect　diagnosis　were　used　to　extract　the　fault　feature　on　the　early　stage.　The　results　showed　that　these　methods　were　very　effective　and　could　provide　the　determination　basis　for　the　predictive　maintenance.