Sweet potato is rich in starch. Following the prosperous development of the sweet potato food market, its sub-quality residue accumulates fast and urgently needs disposal. This study is specially designed to convert sub-quality sweet potato into feed for ruminants. The proper silage preparation methods and proper diet formula for lactating cows and goats were evaluated. Results showed that silage preparation is an economical and feasible method to preserve sub-quality sweet potatoes. Silage from sub-quality sweet potato could substitute the medium amount of corn meal in diets for cows and goats and maintain good milking performance. Conversion of local agricultural and processing by-products not only increases self-produced feed resources and thus enhances feed security, but also cuts down on environmental pressure in handling the waste. Furthermore, the effective conversion stimulates agricultural recycling and reduces carbon emissions.