The invention relates to a soft package membrane for a lithium battery. The soft package for the lithium battery membrane is sequentially provided with a nylon layer, a polyurethane adhesive layer, an aluminum foil layer, a preservative treatment layer, a bonding resin layer and a hot sealing layer. The soft package membrane is characterized in that a protective layer is further arranged between the preservative treatment layer and the bonding resin layer; the protective layer contains cage-like silsesquioxane which accounts for 2-8wt% of the total weight; the cage-like silsesquioxane consists of hydroxyl cage-like silsesquioxane and epoxy cage-like silsesquioxane in a weight ratio of 0.1: 1 to 0.3: 1. The soft package membrane for the lithium battery provided by the invention has good scour depth-resisting performance on the premise of satisfying the practical performance.