A successive 5-year field experiments were designed to study the effects of different treatments of Chinese milk vetch and rice straw on rice yield, agricultural character and economic benefit at purple soil region in Dongting Lake. Compared to F100, the results showed that different treatments of Chinese milk vetch and rice straw could maintain a stable or slight yield increase under the reduction of 20% chemical fertilizer application. The synergistic effects of Chinese milk vetch and rice straw had advantage over the single treatments of Chinese milk vetch or rice straw on rice yield increase. Synergistic treatment of F80+HR+A, one of Chinese milk vetch + rice straw treatments, was more suitable for increasing 5-year average yield for early, later rice, net income and the rate of remuneration of marginal cost, they were 20.2%, 11.9%, 13.7% and 3.4 Yuan/Yuan respectively, which were greater than that of F100 with the difference reached to the significant level (P<0.05). The increase of plant height, filled grain number per panicle, 1000-grain weight in early rice and plant height, efficient panicle, filled grain number per panicle in later rice were the main contributions to high rice yield. Returning high pile of straw and planting Chinese milk vetch in winter not only increased rice yield, but also achieved the best economic benefits, as well as reduced the amount of chemical fertilizer.