Precision irrigation is the new generation irrigation system that have tremendous potential to improve water control. this paper presents decision support system for precision irrigation in which sensor-grid technology is used to assist irrigation management decisions. besides, this paper also explains the definition of precision irrigation and its benefits in irrigation managements system. the agriculture is depended on quantity and quality of water. the main problem of water quantity is how to consider the water resources like dam or river, irrigation infrastructure and rain condition. the methodology to establish large-scale remote intelligent irrigation system based on sensor-grid by using wireless sensor netwrok and considering grid climate stations.