Optimal crop pattern is necessary information for farmer who used to be the guidelines at the beginning of cultivation. This study used an allocation LP model that can take into account heterogeneity of crop water requirement and crop yield of irrigation area for finding optimal crop pattern. A sensitivity analysis of irrigation efficiency in the modified LP model was accounted in the study. The proposed model was applied to find the optimal crop pattern of the Huai-Ang Irrigation Project where located in the Northeast Region of Thailand during dry-season (Mid December-Mid April). The records of seasonal flow, requested and actual irrigation areas, crop water requirement, crop yield, evaporation and effective rainfall of the project were used for this illustrative application. Results showed that the modified LP model is feasible for finding the optimal crop pattern. Heterogeneous character in allocation LP model provided the crop pattern that suitable for cultivating crop on the actual land area. The consideration of vary irrigation efficiency in irrigation planning provided the optimal crop pattern that can be given the higher gross benefit.