If that is of any help to you @caizhikun, here is how I do it:

// called each time my hero is created or change his equipment. 
public void updateSkin() {
    skeletonAnimation.Skeleton.SetAttachment("weapon", "melee/" + Equipment.get("weapon"));
    skeletonAnimation.Skeleton.SetAttachment("shield", "shield/" + Equipment.get("shield"));
    skeletonAnimation.Skeleton.SetAttachment("bow", "range/" + Equipment.get("bow"));
    // etc. idem for armor
    // In my real code I use Constants as Identifier (less error prone)
}

Equipment is just a Class that store different strings according to what my hero is currently supposed to wear.

The cool part is, I have put the images used by Spine in Resource file of Unity (eg "Resource/skin/melee/swordIron"). Which means I can also load those image for my Equipment Menu icon for example.