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Hetao irrigation district in Inner Mongolia was selected as the study site. The domination principle of synergetic was used for analysis. Order parameters were established in three subsystems of the plantation system: resources environment, socio economic and plantation structure subsystem, respectively. The order degree and coordination degree of the system from 1960 to 2008 were calculated by a system identification model based on synergetic theory. Furthermore, the changes on the coordinating degree were analyzed as well as the synergy and difference features. The threshold values were then put forward for informing reasonable plantation structure. The results show that the coordination degree of the plantation system presents fluctuation changes, but the changes are relatively low. Particularly, a break occurred in 2004 and shows significantly difference characteristics. Finally, a reasonable threshold interval of proportion for crop plantation was put forward. It is grain (47.82%,，62.66%) and economic crops (24.64%,，43.49%). 