We used the single-factor full-randomized design of the experiment,selected 700 10-day old Lijia ducks which are healthy and similarly weighted, and allocated to 7 treatments randomly, 2 repetitions for each treatment, and 50 ducks for each repetition. In order to study the effects of different proportions of cottonseed meal and rapeseed meal as a full substitution for soybean meal on production performance of ducks, and determination of the most optimal supplementary levels of cottonseed meal and rapeseed meal in ducks diet. We did the rearing and slaughter experiment,analyzed the economic profit.The results were showed that the different proportions of cottonseed meal and rapeseed meal as a full substitution for soybean meal has a significant influence on the growing performance of ducks, but has no negative effect on slaughter performance. The daily gain of ducks was reduced as the proportion of rapeseed meal increase and cottonseed meal decrease, while the daily intake of ducks was first reduced and then increased as the proportion of cottonseed meal increase. If the proportion of cottonseed meal and rapeseed meal is suitable, the cottonseed meal and rapeseed meal as a full substitution for soybean meal is feasible. Under these experimental conditions, the most optimal supplementary levels of cottonseed meal and rapeseed meal are 11% and 8%.