A system and method for optimal allocation of agricultural water based on water consumption control are provided. The system includes a data management module, configured to store and manage data related to water allocation; a basic data statistics module, configured to take statistics on various stored data; an agricultural evapotranspiration (ET) calculation module, configured to calculate an agricultural ET based on the stored data and statistical data; and a water resource allocation module, configured to generate a corresponding water resource allocation scheme based on an agricultural ET of each water consumption unit and corresponding data. Surface water and groundwater are jointly allocated to reduce groundwater exploitation, increase groundwater recharge, reduce invalid water loss and consumption in a carrying and allocation process, and improve an output benefit of agricultural water supply. This provides technical support for realization of agricultural target ETs in different hydrologic years and sustainable utilization of water resources.