NOVELTY - Flexible metal substrate connected with back electrode of solar battery comprises stainless steel band as substrate having one side plated with conducting layer and multilayer diffusion barrier layer. The conducting layer is copper coating. The multilayer diffusion barrier layer comprises greater than or equal to 2 layers of nickel coating and greater than or equal to 2 layers of nickel molybdenum alloy coating in sequence. The nickel coating is connected with copper coating; and the nickel molybdenum alloy coatings are connected with the back electrode.    USE - Flexible metal substrate connected with back electrode of solar battery, i.e. copper indium gallium selenide (CIGS) solar battery.    ADVANTAGE - Diffusion of iron element in copper and steel bands is prevented; and new harmful elements are not introduced at the same time. The nickel molybdenum alloy with high molybdenum content improves the binding force of substrate and back electrode layer. The copper layer is used as main current conducting layer, so that the molybdenum layer is just used as back contact layer in good ohmic contact with the absorption layer. Thus, by using the flexible metal substrate as substrate of CIGS solar battery, the thickness requirement of molybdenum layer can be reduced greatly. The flexible metal substrate can be produced on continuous electroplating production line at low cost and high efficiency.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for preparation of flexible metal substrate comprising performing surface pretreatment to stainless steel band before plating; placing the processed steel band in a plating groove; electroplating copper coating with thickness of 1-3 mu m at one side; electroplating greater than or equal to 2 layers of nickel coating on the copper coating; and electroplating greater than or equal to 2 layers of nickel molybdenum alloy coating with molybdenum content increasing from 10% to 80% in the coating growth direction layer by layer gradually on the nickel coating.