This article analyzed the different impacts of Russia Belarus Kazakhstan (RBK) custom union on agricultural products trade of the whole China and Xinjiang with regression model, then analyzed inefficiency part by the Stochastic Frontier Gravity Model and the gray model, and predicted the tendency of the impact. Result shows that RBK has inhibitory effect on Chinese agricultural export trade, which is especially obvious to Xinjiang; inefficiency level of the trade trends to decline, trade efficiency factor will weaken the negative impact of RBK custom union. Agricultural export trade continues going up yearly over the next four years, growth rate of Xinjiang is much higher; to Xinjiang, RBK custom union is both opportunity and challenge, but there are more opportunities than challenges. Combining main conclusions, we put forward policy suggestions.